Effects of drought on water content and photosynthetic parameters in potato plants expressing the trehalose-6-phosphate synthase gene of Saccharomyces cerevisiae

Two transgenic potato lines, T1 and T2, expressing the trehalose-6-phosphate synthase (TPS1) gene of yeast were isolated. In our experimental approach, we applied two novelties, namely the fusion of the drought-inducible promoter StDS2 to TPS1 and a marker-free transformation method. In contrast to the expected drought-induced expression, only a very low constitutive TPS1 expression was detected in the transgenic lines, probably due to chromosomal position effects. The observed expression pattern, however, was sufficient to alter the drought response of plants. Detached leaves of T1 and T2 showed an 8 h delay in wilting compared to the non-transformed control. Potted plants of T1 and T2 kept water 6 days longer than control plants and maintained high stomatal conductance and a satisfactory rate of net photosynthesis. During drought treatment, CO₂ assimilation rate measured at saturating CO₂ level was maintained at maximum level for 6–9 days in transgenic plants while it decreased rapidly after 3 days in the wild type plants. Under optimal growth conditions, lower CO₂ fixation was detected in the transgenic than in the control plants. Stomatal densities of T1 and T2 leaves were reduced by 30–40%. This may have contributed to the lower CO₂ fixation rate and altered drought response. Ibolya Stiller, and Sándor Dulai contributed equally to this work.     

Size selectivity of aqueous pores in stomatous cuticles of <Emphasis Type="Italic">Vicia faba</Emphasis> leaves

Size selectivity of aqueous pores in Vicia leaf cuticles was investigated by measuring the penetration of calcium salts into the abaxial surface of detached leaves. Molecular weights of salts ranged from 111 g mol^–1 to 755 g mol^–1. Penetration in light at 20°C and 100% humidity was a first order process and rate constants of penetration ranged from 0.39 h^–1 (CaCl₂) to 0.058 h^–1 (Ca-lactobionate). Penetration was a first order process in the dark as well, but the rate constants were smaller by a factor of 1.82. Plotting logarithmatised rate constants versus anhydrous molecular weights resulted in straight lines both in light and in the dark. The slopes per hour were very similar and the average slope was –1.2×10^–3 mol g^–1. Hence, size selectivity was not affected by stomatal opening, and in light or darkness permeability of Vicia cuticles decreased by a factor of 2.9 when molecular weight increased from 100 g mol^–1 to 500 g mol^–1. Silver nitrate was preferentially precipitated as silver chloride in guard cells, glandular trichomes and at the base of trichomes. It was concluded that these precipitates mark the location of aqueous pores in Vicia leaf cuticles. The size selectivity of aqueous pores in Vicia leaf cuticles is small compared to that observed in poplar leaf cuticles, in which permeability decreased by a factor of 7–13 for the same range of molecular weights. It is also much smaller than size selectivity of the lipophilic pathway in cuticles. These findings suggest that active ingredients of pesticides, growth regulators and chemical inducers with high molecular weights penetrate leaves at higher rates when formulated as ions.     

High temperature effects on photosynthetic activity of two tomato cultivars with different heat susceptibility

The functional activities of the photosynthetic apparatus of two tomato cultivars of different thermotolerance were investigated after a short period of high temperature treatment. Seedlings of two tomato genotypes, Lycopersicon esculentum var. Campbell-28 and the wild thermotolerant Nagcarlang, were grown under a photoperiod of 16h at 25 degrees C and dark period of 8h at 20 degrees C. At the fourth true leaf stage, a group of plants was exposed to heat stress of 45 degrees C for 2 h. The heat shock treatment caused important reductions of the net photosynthetic rate (Pn) of Campbell-28 plants due to non-stomatal components. These non-stomatal effects were not evident in Nagcarlang-treated plants. This reduction in the CO2 assimilation rate observed in Campbell-28 was generated by affections in the Calvin cycle and also in the PSII functioning. No changes in these parameters were observed in the thermotolerant genotype after the stress. Injury to the plasma membrane because of the heat stress was evident only in the Campbell-28 genotype. Heat led to a sun-type adaptation response of the photosynthesis pigment apparatus for the Nagcarlang genotype, but not for Campbell-28, and thus an increase in chlorophyll a/b ratio and a decrease in chlorophyll/carotenoid ratio were shown in Nagcarlang stressed plants.     

Some Physiological and Morphological Responses in Flooded Maize

After flooding of maize seedlings for fourteen days, their stomata were closed, and total nucleic acid was accumulated in subwater knots before adventitious roots appeared. Aerenchyma were developed and some physiological and morphological changes were induced in fourweek old Zea mays L. seedlings. It aeems possible that the maize seedlings had adapted to the flood circumstances by forming adventitious roots on submerged knots of the stems, which was not only thick and white but also with no root hairs and grew upwards.     

Water Vapour Diffusion in the Substomatal Cavity

In this paper stomatal pore and substomatal cavity are considered to be elliptic cylinders, A three-dimensional diffusion model is presented, which describes the diffusion of vapour from the surfaces of the cells surrounding the cavity to the outer end of the pore Equations describing vapour diffusion in the model are set up, based on Fick's law and the law of conservation of mass, and are solved by using computer. Quantitative relation between the cavity resistance to water vapour diffusion and: stomatal aperture is obtained and is given more general theoretical explanation. Comparing the formula obtained in this paper with those of Brown and Escombe and of Cooke et al., it is found that the cavity resistance calculated by the latter two formulas are 0.5 to 1 times higher in a large rankle of stomatal aperture values. Besides, it is shown by calculating that the rates of loss from guard cells and subsidiary ceils account for 88%– 93% and 7%–12% respectively of that from epidermic cells, and the litter amounts to 86%–96% of that from all the cells in the cavity in the large range of stomatal change.     

中国葡萄属植物叶片气孔特征的研究

对起源于中国的葡萄属(Vitis L.)20个种或变种叶片气孔特性进行了观察研究。结果表明:气孔纵径对葡萄属种的分类有较大的价值;气孔比密度(叶片上所有气孔复合体面积与叶片面积之比)与叶片大小呈极显著正相关;气孔密度与气孔纵径呈极显著负相关;所有观察种类的叶片气孔类型均为不规则型。     

Field comparisons of photosynthesis and leaf conductance in Ziziphus mauritiana and other fruit tree species in Zimbabwe

 Data are presented for gas exchange in exposed leaves in field grown Ziziphus mauritiana (Lamk.) at a highland site and potted seedlings at a hotter lowland site in tropical Zimbabwe, together with indigenous and locally-grown commercial fruit crops. The field trial at the highland site included local Ziziphus mauritiana, introduced Indian Z. mauritiana (cv. Umran), fig and peach. In all species assimilation was highest early in the morning, followed by a gradual decline throughout the remainder of the day. Leaf conductance followed the same trend as assimilation for fig and peach, but in Ziziphus cv. Umran and Ziziphus Musau, conductance tracked irradiance, reaching a maximum in the middle of the day. In all species, sub-stomatal CO₂ concentrations increased with declining assimilation indicating that during high irradiance, assimilation was mainly controlled by mesophyll limitations rather than conductance. At the highland site both Ziziphus cv. Umran and Musau were highly productive, with light saturated assimilation significantly higher than in either fig or peach (P < 0.01). At the warmer lowland site, assimilation and conductance in Ziziphus Musau were also higher than in other indigenous fruit tree species growing under similar conditions. Despite increased assimilation in Ziziphus, when compared to the other species, there was no increase in the assimilation ratio (ratio of assimilation/conductance) which was offset by the high conductance values. The data indicate that under conditions where water was not limiting, young Ziziphus showed no enhanced stomatal control over water loss, but was highly productive (per unit leaf area) relative to the other species. Received: 17 October 1996 / Accepted: 8 January 1997     

陆生植物气孔参数与大气CO_2浓度变化

陆生植物的起源与演化与全球气候和环境的变化密不可分,利用植物气孔参数(气孔密度和气孔指数)来指示或重建古大气CO2浓度变化是近年来全球变化研究的热点之一。就陆生植物气孔参数的研究进行了概述,对研究中存在的问题及其前景作了简要探讨,并对植物生物学方法在定量研究古气候和古环境变化的趋势进行了分析。     

地黄属（Rehmannia）和崖白菜属（Triaenophora）植物的叶表皮形态特征

利用扫描电子显微镜对车前科(P lantaginaceae)地黄属(Rehmannia)和崖白菜属(Triaenophora)8种植物成熟叶片的背面进行了观察。地黄属和崖白菜属的气孔都突出于叶表面,气孔类型均为无规则型;毛被有2种类型,即单列多细胞疏柔毛 单列多细胞腺毛和单列多细胞棉毛 单列多细胞腺毛。气孔和毛被在种间无明显的差异,不能作为分种依据,但毛被在属间具有明显的差异,具有一定的属间分类意义。