无机营养对春小麦抗旱适应性的影响

本文研究了无机营养对春小麦一些抗旱适应性的影响,主要包括:渗透调节的大小和变化过程、可溶性糖的积累、脯氨酸的积累、叶片导度的变化、离体叶片的失水速率、叶面积和耗水量的变化、根系生长和根/植冠值,并且分析了各个处理植株的水分利用效率(WUE)和产量的变异。认为,在干旱条件下,无机营养对于春小麦不同器官、不同生理功能,并不都具有一致的作用。有的利于提高植株的抗旱性,有的可以改变一些适应性产生的时间和发展过程,有的则不利于植株的抗旱性。通过综合分析,提出旱地施肥使作物增产的主要原因是,营养元素满足了作物生长所需,促进了根系发育,利于吸收水分、维持水分平衡和正常生理功能,但对作物自身的耐旱性并没有产生显著影响。     

CARBOHYDRATE PHYSIOLOGY OF ORCHID SEEDLINGS. III. HYDROLYSIS OF MALTOOLIGOSACCHARIDES BY PHALAENOPSIS (ORCHIDACEAE) SEEDLINGS

Germinating seeds and developing seedlings of Phalaenopsis Habsburg and Phalaenopsis Ruth Burton × (Phalaenopsis Abendrot × Phalaenopsis Abendrot) can utilize glucose, maltose, maltotriose, maltotetraose, maltopentaose, maltohexaose, and maltoheptaose as carbon sources. Fresh weight decreased significantly with increased polymerization from glucose through maltoheptaose. Seedling survival declined on higher molecular weight sugars reaching levels which were significantly different from those on glucose. Sugar uptake increased moderately with increasing molecular weight of oligomers. The maltooligosaccharides used in these experiments are hydrolyzed by the orchid seedlings and of the sugars which can support good growth glucose, but not maltose accumulate in culture media. As a result, media which supported seedlings contained substantial levels of glucose, the starting sugars, and decreasing amounts of the next shorter oligomers. This suggests enzymatic endwise hydrolysis of these maltooligosaccharides. Similar results were obtained with Phalaenopsis seedlings produced from seeds which were germinated on sugar-free medium and transferred to a solution containing the same oligomers. Sugars in media which did not support seedlings were not hydrolyzed.     

THE ROLE OF NITROGEN NUTRITION IN HIGH-TEMPERATURE TOLERANCE OF THE KELP,LAMINARIA SACCHARINA (CHROMOPHYTA)1

Mechanisms of high-temperature tolerance in the kelp Laminaria saccharina (L.) Lamour. were examined by comparing a heat-tolerant ecotype from Long Island Sound (LIS), New York, and a population from the Atlantic (ATL) coast of Maine. Greater heat tolerance was not attributable to greater thermal stability of the photosynthetic apparatus: LIS and ATL plants exhibited similar short-term effects of high temperature on photosynthetic capacity (P_max) and quantum yield (estimated as the ratio of variable to maximum chlorophyll fluorescence, F_v/F_m. As LIS plants had consistently higher N and protein content than ATL plants, the interaction between nitrogen nutrition and high-temperature tolerance was examined. When grown under high N supply and optimal temperature (12° C), LIS plants had a higher density of photosystem II reaction centers (RCII), higher activity of two Calvin cycle enzymes (ribulose bisphosphate carboxylase oxygenase [RUBISCO] and NADP-dependent glyceraldehyde-3-phosphate dehydrogenase [G3PDH]), and higher P_max and F_v/F_m than ATL plants. Individual ATL plants, furthermore, exhibited close correlations of RCII density and enzyme activity with N and/or protein content. Variation in RCII density and enzyme activity, in turn, largely accounted for plant-to-plant differences in P_max and F_v/F_m. Relationships among these parameters were generally weak or lacking among individual LIS plants grown under optimal conditions, apparently because luxury N consumption resulted in excess reserves of photosynthetic apparatus components. Exposure of N-replete LIS and ATL plants to a superoptimal temperature (22° C) for 4 days caused an increase in the minimum turnover time of the photosynthetic apparatus (tau) and a decrease in P_max, but had no consistent effect on F_v/F_m RCII density, PSU size (chlorophyll a/RCII), or enzyme activities. When plants were subjected to concurrent N limitation and heat stress, however, LIS and ATL populations exhibited quite different responses. All photosynthetic parameters of N-limited ATL plants declined sharply in response to high temperature, resulting in a negative rate of daily net C fixation. In contrast, LIS plants showed a reduction in PSU size, but maintained other parameters, including daily C fixation, at levels similar to those of N-limited plants at optimal temperature. Overall, the ability of LIS plants to accumulate and maintain high N reserves appears to be critical for heat tolerance and, therefore, for survival during summer periods of simultaneous low N supply and superoptimal temperature. ATL plants, which also experience low summer N supply but not superoptimal temperatures, do not accumulate large reserves of nitrogenous components and are unable to tolerate the combined stress. Because low N supply often co-occurs with high temperatures in temperate marine systems, large-scale declines in algal productivity, such as during El Niño events, are probably due to the interactive effect of N limitation and heat stress.     

SOME EFFECTS OF NITROGEN NUTRITION ON THE MORPHOLOGY AND ANATOMY OF MARROW-STEM KALE

Marrow-stem kale plants grown on plots receiving frequent additions of sulphate of ammonia showed a 40% increase in length of internode and a 25% increase in number of nodes per plant, and the leaf size was increased by between 50 and 70% over plants in plots receiving no N fertilizer. Leaves of kale continue to increase in area until they turn yellow, and the high N leaves showed a greater rate of increase in area at every stage in the life of the leaf.
Various features of leaf structure, such as stomatal index, and thickness of palisade and mesophyll, were unaffected by N treatment. The size of the epidermal cells of the leaves was very variable, and although the high N leaves showed a 12% increase in area per epidermal cell over the low N leaves, this difference is not statistically significant. The increased area of the high N leaves can therefore be attributed mainly to increased cell division during the life of the leaf. Only a very slight increase in rate of cell division is necessary to produce the observed effect.
The greater leaf area of the high N plants can be attributed mainly to increased size of individual leaves, but there was also a significantly greater number of living functional leaves per plant on the high N plants; at 23 weeks from sowing the high N plants had an average of 13.4 living leaves, while the low N plants had only 11.7 living leaves per plant.
There was an appreciable degree of N succulence in the high N kale leaves, which showed a 2% greater moisture content than the low N leaves.
A seasonal drift in epidermal cell size, palisade thickness, and total leaf thickness, is shown to be fully significant, statistically. Marked variations in stomatal frequency are barely significant at the 5% level.     

CARBOHYDRATE PHYSIOLOGY OF ORCHID SEEDLINGS. II. HYDROLYSIS AND EFFECTS OF OLIGOSACCHARIDES

Orchid seedlings were grown on nutrients containing cold-sterilized sugars as sources of carbon. Action by an extra-cellular invertase was implied from the hydrolysis by seedlings of sugars containing α-D-glucopyranosyl-(1 → 2)-β-D-fructofuranoside bonds. D-galactosides (α and β) were also hydrolyzed, indicating the presence of extracellular galactosidases. Hydrolysis of α-D-fructofuranosides and α-D-galactosides decreased with increasing molecular weight. Seedling damage and growth retardation were paralleled by galactose accumulation in the substrate. Rupture of tonoplast and evagination of the nuclear envelope suggests that this sugar may alter some factor(s) responsible for the maintenance of membrane permeability.     

金鱼藻抗氧化酶对水体无机氮升高的响应

为了研究水体富营养化引起的无机氮升高对沉水植物的胁迫 ,本研究用 4种浓度的碳酸铵和 5种浓度的硝酸钾对金鱼藻进行急性处理 ,分别在 5— 4 8h内测定植株超氧化物歧化酶 (SOD)、过氧化氢酶 (CAT)、过氧化物酶(POD)和抗坏血酸过氧化物酶 (APX)的活力。结果表明铵盐处理下 4种酶中CAT活性变化最大 ,在 5— 15h时其活性与处理浓度正相关。更长时间 2 4h处理则导致响应停止。硝酸盐处理下SOD、APX和CAT活性在 2 4h时才有明显升高。SOD和CAT活性在 4种酶中变化最大 ,它们对处理浓度变化的响应趋势都是在低浓度处理上升然后在较高浓度下降。在铵盐和硝酸盐处理下APX活性都是在 4种酶中最低 ,其变化规律与CAT相当一致。本研究表明CAT对铵盐胁迫响应较快 ;SOD和CAT对硝酸盐胁迫的响应速度较铵盐慢 ;这两种抗氧化酶可作为检验无机氮浓度升高对沉水植物胁迫的敏感指标