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- Author or Editor: L. V. Gusta x
- HortScience x
Plants acclimate to abiotic stresses, e.g. heat, freezing drought and salinity, in response to environmental cues such as temperature, daylength and water. Plants can respond within minutes to the cue e.g. heat tolerance or within hours or days, e.g. drought and freezing tolerance. Heat shock proteins are measurable within 20 to 30 minutes of a heat stress and the plants aclimate almost immediately. In contrast, proteins related to freezing tolerance are measurable within hours but days are required before a measurable increase in freezing tolerance can be detected. In almost all stresses it appears that the environmental cue effects the water status of the plant which in turn affects the level of endogenous abscisic acid (ABA). ABA has been implicated to ameliorate the stress by inducing genes to produce stress proteins. There is a certain degree of commodity between stresses in ragards to stress proteins, however each stress has their own unique set of stress proteins. For example heat shock proteins did not confer stress tolerance. Proteins involved in water and osmotic stress tolerance share a high degree of commonality. I” all stresses a unique class of proteins are synthesized which are classified as heat or boiling stable (do not coagulate at 100°). These proteins are suggested to be involved in the stress response. Many of these heat stable proteins are induced by ABA alone or in combination with jasmonic acid (JA). Analogs of ABA which are either slowly converted to ABA or are degraded slowly or taken up at a faster rate than ABA have been tested for the efficacy in inducing the stress responses. Analogs have also been identified which inhibit the ABA induced response. How these analogs may have practical significance will be discussed.
Abstract
The supercooling of flower primordia within dormant peach buds [Prunus persica (L.) Batsch.] is dependent on water migration from the base of the flower primordium to preferential sites of freezing in the flower bud scales and pith during the initial stages of freezing. The preferential freezing that occurs in the flower bud scales and pith does not appear to be caused by a difference in distribution of ice nucleators. The mean nucleation temperature of the flower bud increased with the amount of attached shoot, an indication that ice nucleation began in the shoot and spread into the flower bud. The flower primordium, however, appeared to have an intrinsic resistance to ice nucleation in comparison to other parts of the flower bud, which may be related to its lower water and osmotic potentials. The reduced osmotic potential of the flower primordium could be a consequence of significantly higher sucrose levels on a dry weight basis compared to that of the vascular tissue below the flower buds or that of the flower bud scales. A gradient in water potential between the xylem of the shoot and the flower bud also existed and may account for the recovery of water that is lost from the flower bud during freezing.
Abstract
A freezer system is described for subjecting biological materials to temperatures between +50° and -85°C. The system provides for removal of latent heat of fusion, adjustment of tissue water content, uniformity of temperature, control of supercooling and a wide range of cooling rates.
Seeds of celery, spinach, onion, cress, water cress, iceberg lettuce, Great Lakes lettuce, cabbage, tomato, sweet corn and celery were pre-treated with 0.1 μM/g seed of both ABA and analogs of ABA. The chemicals were dissolved in a mixture of methanol:hexane (9:1/v:v) and applied to the seeds for approximately 3 minutes. The solvent was removed from the seeds within 5 minutes by rotary evaporation under reduced pressure. Effects on petri plate germination and soil emergence were monitored daily at 5, 10 and 15°C. The methanol/hexane solvent alone improved spinach seed emergence at 10°C from 10% to 100% and from 50% to 90% at 15°C in celery. Certain ABA analogs reduced time to 50% emergence in celery by at least 7 days at 15°C. Two ABA analogs synchronized emergence in celery and effect was temperature-dependent. One analog improved seed germination in tomato from 15% to 90% at 10°C. In most cases treatment effects on radicle germination on petri plates was not a good indicator of treatment effects on emergence from a soil based system.
Abstract
The cold hardiness of 6 cool season grass genera was compared in mid-winter under controlled freezing conditions. Creeping bentgrasses (Agrostis palustris Huds.) tolerated the lowest temperatures whereas perennial ryegrasses (Lolium perenne L.) was the least hardy. Kentucky bluegrass (Poa pratensis L.) readily loses cold hardiness when exposed to warm conditions and did not reharden when exposed to cool temperatures. Appreciable hardiness in Kentucky bluegrass was induced by simulating drought conditions.
Abstract
Hydrogen cyanamide or hot-water treatment (47C) for 1 hr at the 250°GS (Growth Stage) effectively broke rest in dogwood buds within 10 to 12 days. At this growth stage, control plants grown at 25/18C (day/night) maintained an LT50 of –25C throughout the 3-week study period, whereas plants treated with H2CN2 or hot water gradually lost hardiness. After 3 weeks at 5/2C (day/night), the control plants hardened to a hardiness (LT50) of –45C, and H2CN2-treated plants maintained an LT50 of –25C. The results demonstrate that the extent of acclimation and deacclimaton of dogwood plants may be influenced by environmental temperatures and rest status.