Decrease In Leaf Water Content Research Articles

Biochemical Changes in Tuber-bearing Solanum Species in Relation to Frost Hardiness during Cold Acclimation

Biochemical changes in potato leaves during cold acclimation have been examined and compared between a frost-tolerant S. acaule and a frost-susceptible S. tuberosum species. Changes were also examined in S. tuberosum, S. acaule, and S. commersonii species when they were hardened at different temperatures to varying hardiness levels.During three weeks of stepwise cold acclimation, S. acaule increased frost hardiness from -6.0 C (killing temperature) to -9.0 C, whereas frost hardiness of S. tuberosum remained unchanged at -3.0 C. Decreases in DNA content on a dry weight basis in both species suggest that matured leaf cells accumulated more dry matter during acclimation. The advantage of using DNA as a reference for comparing metabolite changes during cold acclimation is discussed.Under the stepwise acclimating conditions, both species showed the same trends for increasing total sugar and starch with an insignificant decrease in leaf water content. High levels of total RNA, rRNA, and total and soluble protein were observed in treated S. acaule plants as compared with controls, but not in S. tuberosum. Levels of total lipid and phospholipid also were high in treated S. acaule plants as compared with controls but decreased in S. tuberosum during acclimation.When S. tuberosum, S. acaule, and S. commersonii potatoes were cold-treated at constant day/night temperatures of 10, 5, and 2 C with 14-hour daylength, each species responds differently in terms of frost hardiness increase upon subjecting plants to a low temperature. For instance, after 20 days at 2 C, a net frost hardiness of 3 and 7 C was observed in S. acaule and S. commersonii, respectively, whereas the frost hardiness in S. tuberosum remained unchanged. Also, various levels of frost hardiness can be achieved in a species by subjecting plants to different low temperature treatments. Under a warm regime of 20/15 C day/night temperatures (14-hour light), both S. acaule and S. commersonii can survive at -4.5 C or colder, whereas S. tuberosum can survive only at -2.5 C.Biochemical changes in the leaf tissue of these species were investigated at 5-day intervals during low temperature treatments. Increases in total sugar and starch were found in all three species during hardening, although S. tuberosum failed to harden. Soluble protein contents were increased in both S. acaule and S. commersonii but decreased in S. tuberosum. RNA contents change in a pattern similar to the soluble protein. Net increases of the soluble proteins were positively and significantly correlated with net increases of frost hardiness in S. acaule and S. commersonii.

The Relationship between Environmental Factors and Behaviour of Stomata in the Rice Plants : V. Effects of partial excision of root system on diurnal course of stomatal aperture

The present investigation was undertaken to clarify the relationship between the behaviour of stomata and water absorption through thc roots in rice plants grown under submerged condition by measuring the diurnal course of stomatal aperture in rice plants with partially excised root system. No difference of stomatal aperture was found between plants with non-excised and partially excised root system in early morning when transpiration was not so remarkable and water content of leaf blades was still high (Fig. 2, 3). After about 11 a.m. on a fine day accompanied by intense transpiration, stomata closed to a more considerable extent in plants with partially excised root system than that of non-excised one, due to decrease of water content of leaf blades (Fig. 2, 3). The extent of stomatal closure is severer in lower leaves than in upper ones, especially in plants with partially excised root system, so that the difference of stomatal aperture between lower and upper leaves became larger in the afternoon (Fig. 4, Table 1). Leaf water content on an areal basis followed the diurnal variation pattern of taking the maximum value in early morning and decreasing towards atternoon. The decrease of leaf water content was rather remarkable in plants with partially excised root system than that of non-excised one on fine days, but the difference was smaller than was expected (Fig. 5). Leaf water saturation deficit was different significantly between plants with non-excised and partially excised root system in the afternoon on the fine day at the ripening stage (Table 2). From these results and the close relationship between stomatal aperture and photosynthetic rate, it is suggested that the decrease of water absorption in rice plants grown under submerged condition has much caring on the efficiency of light utilization in photosynthesis because of the stomatal closure in the afternoon on a fine day, in the same manner as the effect of water deficit in the soil.

An analysis of the vertically reflected radiation from a maize crop as a possible means of determining its biomass and water content

A system is described whereby the reflectance frequency distribution found by sensors traversing the top of a maize crop have been used to obtain estimates of the leaf area index and crop water content. Under the conditions investigated it was found that the clearest contrast between the soil and vegetation for leaf area index estimations was obtained in the 700–1100 nm waveband under covered sky conditions. Changes in the pattern of the reflectance frequency distribution with decreasing leaf water content were found in the 1100–2500 nm waveband. The requirements of such a measuring system as revealed by the study are given and possible future improvements together with the need for determinations of this type are discussed.

The relationship between plant sugar concentration, osmotic potential, and frost tolerance in Kharkov MC22 winter wheat. Sugar and frost tolerance

Increased frost survival after exposure of winter wheat seedlings to solutions of glucose, sucrose, or mannitol was not explained simply by changes in the osmotic potential of the leaves. In some cases either an increase in percentage total carbohydrate and reducing sugars, or a slight decrease in leaf water content increased frost survival. Because of the dependency of osmotic potential and percentage total carbohydrate and reducing sugars on the plant's water status, it is difficult to evaluate their individual importance to frost survival. Because maleic hydroxide is residual it does not have application as a short-term (1-week) growth retardant for increasing frost tolerance in winter wheat.

Stomatal responses to changes in humidity in plants growing in the desert

The stomata of plants growing in the Negev Desert, namely the stomata of the mesomorphic leaves of Prunus armeniaca, the xeromorphic stems of Hammada scoparia, and the succulent leaves of Zygophyllum dumosum, respond to changes in air humidity. Under dry air conditions diffusion resistance increases. Under moist air conditions diffusion resistance decreases. When the stomata close at low air humidity the water content of the apricot leaves increases. The stomata open at high air humidity in spite of a decrease in leaf water content. This excludes a reaction via the water potential in the leaf tissue and proves that the stomatal aperture has a direct response to the evaporative conditions in the atmosphere. In all species the response to air humidity is maintained over a period of many hours also when the soil is considerably dry. The response is higher in plants with poor water supply then in well watered plants. Thus for field conditions and for morphologically different types of photosynthesizing organs the results confirm former experiments carried out with isolated epidermal strips.

Detrimental Effect of Rust Infection on the Water Relations of Bean

Bean plants (Phaseolus vulgaris L.) infected with the rust Uromyces phaseoli became unusually susceptible to drought as sporulation occurred. Under the conditions used (1,300 ft-c, 27 C, and 55% relative humidity) such plants wilted at soil water potentials greater than -1 bar, whereas healthy plants did not wilt until the soil water potential fell below -3.4 bars. Determinations of leaf water and osmotic potentials showed that an alteration in leaf osmotic potential was not responsible for the wilting of diseased plants. When diffusive resistance was measured as a function of decreasing leaf water content, the resistance of healthy leaves increased to 50 sec cm(-1) by the time relative water content decreased to 70%, whereas the resistance of diseased leaves remained less than 8 sec cm(-1) down to 50% relative water content. Apparently, water vapor loss through cuticle damaged by the sporulation process, together with the reduction in root to shoot ratio which occurs in diseased plants, upset the water economy of the diseased plant under mild drought conditions.