Michael Dowgert (presenting author) Market Manager Agriculture, Netafim USA, 5470 E. Home Ave, Fr... more Michael Dowgert (presenting author) Market Manager Agriculture, Netafim USA, 5470 E. Home Ave, Fresno CA 93727 Brian Marsh, Superintendent Shafter Research and Extension Center, University of California, 17053 N. Shafter Ave., Shafter, CA. 93263 Robert B. Hutmacher, Cooperative Extension Specialist-Cotton, UC Shafter REC, 17053 N Shafter Ave., Shafter CA 93263 Thomas L. Thompson, Professor of Soil Science, Department of Soil, Water and Environmental Science, University of Arizona, P.O. Box 210038, Tucson, AZ 85721 Dennis Hannaford, Agricultural Product Manager, Netafim USA, 5470 E. Home Ave., Fresno CA 93727 Jim Phene, Automation Manager, Netafim USA, 5470 E. Home Ave., Fresno, CA 93727 Jim Anshutz, Technical Director, Netafim USA, 5470 E. Home Ave., Fresno CA 93727 Claude J. Phene Consulting Scientist, SDI+, 13089 Wiregrass Lane, Clovis, CA 93619
Irrigated agriculture is one of the most critical human activities sustaining civilization. The c... more Irrigated agriculture is one of the most critical human activities sustaining civilization. The current world population of 6.8 billion people is sustained in a large part by irrigated agriculture. USDA statistics show that 17% of cultivated crop land in the United States is irrigated. Yet this acreage produces nearly 50% of total US crop revenues. According to the FAO the approximate 1,260 million ha under rainfed agriculture, corresponding to 80% of the world’s total cultivated land, supply 60% of the world’s food; while the 277 million ha under irrigation, the remaining 20% of land under cultivation, contribute the other 40% of the food supplies. On average, irrigated crop yields are 2.3 times higher than those from rainfed ground. These numbers demonstrate that irrigated agriculture will continue to play an important role as a significant contributor to the worlds food supply.
In conclusion, isolated protoplasts are an excellent arena in which destabilization of the plasma... more In conclusion, isolated protoplasts are an excellent arena in which destabilization of the plasma membrane can be directly observed during a freeze-thaw cycle by cryomicroscopy. Destabilization is manifested in various ways--intracellular ice formation, loss of osmotic responsiveness, or expansion-induced lysis. The incidence of any particular form of injury will depend on the freeze-thaw protocol and hardiness of the tissue from which the protoplasts were isolated. In all cases, however, cold acclimation directly increases the stability of the plasma membrane to the multiple stresses that arise during a freeze-thaw cycle. Such observations provide for functional differences in the plasma membrane that may now be used to consider the significance of any compositional changes in the membrane that might be determined.
Summary The plasma membrane of protoplasts isolated from rye leaves (Secale cereale L. cv. Puma) ... more Summary The plasma membrane of protoplasts isolated from rye leaves (Secale cereale L. cv. Puma) can withstand a maximum elastic stretching of about 2%. Larger area expansions involve the incorporation of new material into the membrane. The dynamics of this process during expansion from isotonic solutions and the probable frequency of lysis have been measured as a function of membrane
When cooled at rapid rates to temperatures between -10 and -30 degrees C, the incidence of intrac... more When cooled at rapid rates to temperatures between -10 and -30 degrees C, the incidence of intracellular ice formation was less in protoplasts enzymically isolated from cold acclimated leaves of rye (Secale cereale L. cv Puma) than that observed in protoplasts isolated from nonacclimated leaves. The extent of supercooling of the intracellular solution at any given temperature increased in both nonacclimated and acclimated protoplasts as the rate of cooling increased. There was no unique relationship between the extent of supercooling and the incidence of intracellular ice formation in either nonacclimated or acclimated protoplasts. In both nonacclimated and acclimated protoplasts, the extent of intracellular supercooling was similar under conditions that resulted in the greatest difference in the incidence of intracellular ice formation-cooling to -15 or -20 degrees C at rates of 10 or 16 degrees C/minute. Further, the hydraulic conductivity determined during freeze-induced dehydration at -5 degrees C was similar for both nonacclimated and acclimated protoplasts. A major distinction between nonacclimated and acclimated protoplasts was the temperature at which nucleation occurred. In nonacclimated protoplasts, nucleation occurred over a relatively narrow temperature range with a median nucleation temperature of -15 degrees C, whereas in acclimated protoplasts, nucleation occurred over a broader temperature range with a median nucleation temperature of -42 degrees C. We conclude that the decreased incidence of intracellular ice formation in acclimated protoplasts is attributable to an increase in the stability of the plasma membrane which precludes nucleation of the supercooled intracellular solution and is not attributable to an increase in hydraulic conductivity of the plasma membrane which purportedly precludes supercooling of the intracellular solution.
Cryomicroscopy of protoplasts isolated from nonacclimated (NA) rye leaves (Secale cereale L. cv P... more Cryomicroscopy of protoplasts isolated from nonacclimated (NA) rye leaves (Secale cereale L. cv Puma) revealed that the predominant form of injury following cooling to the minimum temperature for 50% survival (LT(50)) (-5 degrees C) was expansion-induced lysis of the plasma membrane during warming and thawing of the suspending medium when the decreasing osmolality resulted in osmotic expansion of the protoplasts. When cooled to temperatures below the LT(50), the predominant form of injury was loss of osmotic responsiveness following cooling so that the protoplasts were osmotically inactive during warming. Only a low incidence (<10%) of expansion-induced lysis was observed in protoplasts isolated from acclimated (ACC) leaves, and the predominant form of injury following cooling to the LT(50) (-25 degrees C) was loss of osmotic responsiveness. The tolerable surface area increment (TSAI) which resulted in lysis of 50% of a population (TSAI(50)) of NA protoplasts osmotically expanded from isotonic solutions was 1122 +/- 172 square micrometers. Similar values were obtained when the protoplasts were osmotically expanded from hypertonic solutions. The TSAI determined from cryomicroscopic measurements of individual NA protoplasts was similar to the TSAI(50) values obtained from osmotic manipulation. The TSAI(50) of ACC protoplasts expanded from isotonic solutions (2145 +/- 235 square micrometers) was approximately double that of NA protoplasts and increased following osmotic contraction. Osmotic contractions were readily reversible upon return to isotonic solutions. During freeze-induced dehydration, endocytotic vesicles formed in NA protoplasts whereas exocytotic extrusions formed on the surface of ACC protoplasts. During osmotic expansion following thawing of the suspending medium, the endocytotic vesicles remained in the cytoplasm of NA protoplasts and the protoplasts lysed before their original volume and surface area were regained. In contrast, the exocytotic extrusions were drawn back into the surface of ACC protoplasts as the protoplasts regained their original volume and surface area.
Michael Dowgert (presenting author) Market Manager Agriculture, Netafim USA, 5470 E. Home Ave, Fr... more Michael Dowgert (presenting author) Market Manager Agriculture, Netafim USA, 5470 E. Home Ave, Fresno CA 93727 Brian Marsh, Superintendent Shafter Research and Extension Center, University of California, 17053 N. Shafter Ave., Shafter, CA. 93263 Robert B. Hutmacher, Cooperative Extension Specialist-Cotton, UC Shafter REC, 17053 N Shafter Ave., Shafter CA 93263 Thomas L. Thompson, Professor of Soil Science, Department of Soil, Water and Environmental Science, University of Arizona, P.O. Box 210038, Tucson, AZ 85721 Dennis Hannaford, Agricultural Product Manager, Netafim USA, 5470 E. Home Ave., Fresno CA 93727 Jim Phene, Automation Manager, Netafim USA, 5470 E. Home Ave., Fresno, CA 93727 Jim Anshutz, Technical Director, Netafim USA, 5470 E. Home Ave., Fresno CA 93727 Claude J. Phene Consulting Scientist, SDI+, 13089 Wiregrass Lane, Clovis, CA 93619
Irrigated agriculture is one of the most critical human activities sustaining civilization. The c... more Irrigated agriculture is one of the most critical human activities sustaining civilization. The current world population of 6.8 billion people is sustained in a large part by irrigated agriculture. USDA statistics show that 17% of cultivated crop land in the United States is irrigated. Yet this acreage produces nearly 50% of total US crop revenues. According to the FAO the approximate 1,260 million ha under rainfed agriculture, corresponding to 80% of the world’s total cultivated land, supply 60% of the world’s food; while the 277 million ha under irrigation, the remaining 20% of land under cultivation, contribute the other 40% of the food supplies. On average, irrigated crop yields are 2.3 times higher than those from rainfed ground. These numbers demonstrate that irrigated agriculture will continue to play an important role as a significant contributor to the worlds food supply.
In conclusion, isolated protoplasts are an excellent arena in which destabilization of the plasma... more In conclusion, isolated protoplasts are an excellent arena in which destabilization of the plasma membrane can be directly observed during a freeze-thaw cycle by cryomicroscopy. Destabilization is manifested in various ways--intracellular ice formation, loss of osmotic responsiveness, or expansion-induced lysis. The incidence of any particular form of injury will depend on the freeze-thaw protocol and hardiness of the tissue from which the protoplasts were isolated. In all cases, however, cold acclimation directly increases the stability of the plasma membrane to the multiple stresses that arise during a freeze-thaw cycle. Such observations provide for functional differences in the plasma membrane that may now be used to consider the significance of any compositional changes in the membrane that might be determined.
Summary The plasma membrane of protoplasts isolated from rye leaves (Secale cereale L. cv. Puma) ... more Summary The plasma membrane of protoplasts isolated from rye leaves (Secale cereale L. cv. Puma) can withstand a maximum elastic stretching of about 2%. Larger area expansions involve the incorporation of new material into the membrane. The dynamics of this process during expansion from isotonic solutions and the probable frequency of lysis have been measured as a function of membrane
When cooled at rapid rates to temperatures between -10 and -30 degrees C, the incidence of intrac... more When cooled at rapid rates to temperatures between -10 and -30 degrees C, the incidence of intracellular ice formation was less in protoplasts enzymically isolated from cold acclimated leaves of rye (Secale cereale L. cv Puma) than that observed in protoplasts isolated from nonacclimated leaves. The extent of supercooling of the intracellular solution at any given temperature increased in both nonacclimated and acclimated protoplasts as the rate of cooling increased. There was no unique relationship between the extent of supercooling and the incidence of intracellular ice formation in either nonacclimated or acclimated protoplasts. In both nonacclimated and acclimated protoplasts, the extent of intracellular supercooling was similar under conditions that resulted in the greatest difference in the incidence of intracellular ice formation-cooling to -15 or -20 degrees C at rates of 10 or 16 degrees C/minute. Further, the hydraulic conductivity determined during freeze-induced dehydration at -5 degrees C was similar for both nonacclimated and acclimated protoplasts. A major distinction between nonacclimated and acclimated protoplasts was the temperature at which nucleation occurred. In nonacclimated protoplasts, nucleation occurred over a relatively narrow temperature range with a median nucleation temperature of -15 degrees C, whereas in acclimated protoplasts, nucleation occurred over a broader temperature range with a median nucleation temperature of -42 degrees C. We conclude that the decreased incidence of intracellular ice formation in acclimated protoplasts is attributable to an increase in the stability of the plasma membrane which precludes nucleation of the supercooled intracellular solution and is not attributable to an increase in hydraulic conductivity of the plasma membrane which purportedly precludes supercooling of the intracellular solution.
Cryomicroscopy of protoplasts isolated from nonacclimated (NA) rye leaves (Secale cereale L. cv P... more Cryomicroscopy of protoplasts isolated from nonacclimated (NA) rye leaves (Secale cereale L. cv Puma) revealed that the predominant form of injury following cooling to the minimum temperature for 50% survival (LT(50)) (-5 degrees C) was expansion-induced lysis of the plasma membrane during warming and thawing of the suspending medium when the decreasing osmolality resulted in osmotic expansion of the protoplasts. When cooled to temperatures below the LT(50), the predominant form of injury was loss of osmotic responsiveness following cooling so that the protoplasts were osmotically inactive during warming. Only a low incidence (<10%) of expansion-induced lysis was observed in protoplasts isolated from acclimated (ACC) leaves, and the predominant form of injury following cooling to the LT(50) (-25 degrees C) was loss of osmotic responsiveness. The tolerable surface area increment (TSAI) which resulted in lysis of 50% of a population (TSAI(50)) of NA protoplasts osmotically expanded from isotonic solutions was 1122 +/- 172 square micrometers. Similar values were obtained when the protoplasts were osmotically expanded from hypertonic solutions. The TSAI determined from cryomicroscopic measurements of individual NA protoplasts was similar to the TSAI(50) values obtained from osmotic manipulation. The TSAI(50) of ACC protoplasts expanded from isotonic solutions (2145 +/- 235 square micrometers) was approximately double that of NA protoplasts and increased following osmotic contraction. Osmotic contractions were readily reversible upon return to isotonic solutions. During freeze-induced dehydration, endocytotic vesicles formed in NA protoplasts whereas exocytotic extrusions formed on the surface of ACC protoplasts. During osmotic expansion following thawing of the suspending medium, the endocytotic vesicles remained in the cytoplasm of NA protoplasts and the protoplasts lysed before their original volume and surface area were regained. In contrast, the exocytotic extrusions were drawn back into the surface of ACC protoplasts as the protoplasts regained their original volume and surface area.
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