Carbon Isotope Discrimination,Gas Exchange,and Growth of Sugarcane Cultivars under Salinity

Physiological features associated with differential resistance to salinity were evaluated in two sugarcane (Saccharum spp. hybrid) cultivars over an 8-week period during which greenhouse-grown plants were drip-irrigated with water or with NaCI solutions of 2, 4, 8, or 12 decisiemens (dS) m-1 electrical conductivity (EC). The CO2 assimilation rate (A), stomatal conductance (g), and shoot growth rate (SGR) began to decline as EC of the irrigation solution increased above 2 dS m-1. A, g, and SGR of a salinity-resistant cultivar (H69-8235) were consistently higher than those of a salinity-susceptible cultivar (H65-7052) at all levels of salinity and declined less sharply with increasing salinity. Carbon isotope discrimination ([delta]) in tissue obtained from the uppermost fully expanded leaf increased with salinity and with time elapsed from the beginning of the experiment, but [delta] was consistently lower in the resistant than in the susceptible cultivar at all levels of salinity. Gas-exchange measurements suggested that variation in [delta] was attributable largely to variation in bundle sheath leakiness to CO2 ([phi]). Salinity-induced increases in [phi] appeared to be caused by a reduction in C3 pathway activity relative to C4 pathway activity rather than by physical changes in the permeability of the bundle sheath to CO2. A strong correlation between [delta] and A, g, and SGR permitted these to be predicted from [delta] regardless of the cultivar and salinity level. [delta] thus provided an integrated measure of several components of physiological performance and response.     

Leaf water relations and maintenance of gas exchange in coffee cultivars grown in drying soil

Plant water status, leaf tissue pressure-volume relationships, and photosynthetic gas exchange were monitored in five coffee (Coffea arabica L.) cultivars growing in drying soil in the field. There were large differences among cultivars in the rates at which leaf water potential (Ψ_L) and gas exchange activity declined when irrigation was discontinued. Pressure-volume curve analysis indicated that increased leaf water deficits in droughted plants led to reductions in bulk leaf elasticity, osmotic potential, and in the Ψ_L at which turgor loss occurred. Adjustments in Ψ_L at zero turgor were not sufficient to prevent loss or near loss of turgor in three of five cultivars at the lowest values of midday Ψ_L attained. Maintenance of protoplasmic volume was more pronounced than maintenance of turgor as soil drying progressed. Changes in assimilation and stomatal conductance were largely independent of changes in bulk leaf turgor, but were associated with changes in relative symplast volume. It is suggested that osmotic and elastic adjustment contributed to maintenance of gas exchange in droughted coffee leaves probably through their effects on symplast volume rather than turgor.     

Influence of leaf water status on stomatal response to humidity,hydraulic conductance,and soil drought in Betula occidentalis

Whole-canopy measurements of water flux were used to calculate stomatal conductance (g _s ) and transpiration (E) for seedlings of western water birch (Betula occidentalis Hook.) under various soil-plant hydraulic conductances (k), evaporative driving forces (ΔN; difference in leaf-to-air molar fraction of water vapor), and soil water potentials (Ψ_s). As expected, g _s dropped in response to decreased k or Ψ_S, or increased ΔN(> 0.025). Field data showed a decrease in mid-day g _s with decreasing k from soil-to-petiole, with sapling and adult plants having lower values of both parameters than juveniles. Stomatal closure prevented E and Ψ from inducing xylem cavitation except during extreme soil drought when cavitation occurred in the main stem and probably roots as well. Although all decreases in g _s were associated with approximately constant bulk leaf water potential (ψ_l), this does not logically exclude a feedback response between Ψ_L and g _s . To test the influence of leaf versus root water status on g _s , we manipulated water status of the leaf independently of the root by using a pressure chamber enclosing the seedling root system; pressurizing the chamber alters cell turgor and volume only in the shoot cells outside the chamber. Stomatal closure in response to increased ΔN, decreased k, and decreased Ψ_S was fully or partially reversed within 5 min of pressurizing the soil. Bulk Ψ_L remained constant before and after soil pressurizing because of the increase in E associated with stomatal opening. When ΔN was low (i.e., < 0.025), pressurizing the soil either had no effect on g _s , or caused it to decline; and bulk Ψ_L increased. Increased Ψ_l may have caused stomatal closure via increased backpressure on the stomatal apparatus from elevated epidermal turgor. The stomatal response to soil pressurizing indicated a central role of leaf cells in sensing water stress caused by high ΔN, low k, and low Ψ_S. Invoking a prominent role for feedforward signalling in short-term stomatal control may be premature.     

Associations between partitioning of carboxylase activity and bundle sheath leakiness to CO2, carbon isotope discrimination, photosynthesis, and growth in sugarcane

Genetic and environmental variation in carbon isotope discrimination(     

烟草黄矮双生病毒中双向启动子的活性及其调节控制

将烟草黄矮双生病毒（ＴｏｂＹＤＶ）中双向启动子的区域,以不同长度的片段和方向插入启动子分析载体ｐＧ１,与ＧＵＳ报道基因和ＮＯＳ终止子融合。同时,将各个ＴｏｂＹＤＶ读码框区域插入表达载体ｐＡＲＴ７中,置于ＣａＭＶ３５Ｓ启动子和ＯＣＳ终止子之间。用电穿孔法将各种启动子构建物个别地或者与读码框构建物成对地导入烟草和玉米原生质体,以考察ＴｏｂＹＤＶ启动子控制下ＧＵＳ基因瞬间表达的活性,以及ＴｏｂＹＤＶ的读