Use of lysophosphatidylethanolamine, a natural lipid, to retard tomato leaf and fruit senescence

We studied the influence of lysophosphatidylethanolamine (LPE) on the pattern and rate of ethylene production and respiration of tomato ( Lycopersicon esculentum cv. H7155) leaflets and fruit. Leaflets that had been senescing on the plant showed a climacteric-like rise in ethylene production but not in respiration rate which decreased continuously with leaf age. Detached leaflets had a climacteric-like pattern in respiration whether they were incubated in complete darkness or in light. Detached leaflets incubated in the dark had higher rates of ethylene production and CO₂ evolution than did light-incubated leaves. There was no change in the pattern of ethylene production or CO₂ evolution as a result of LPE treatment. However, LPE-treated attached and detached leaflets had consistently lower rates of CO₂ evolution. The reduction in CO₂ evolution by LPE was most pronounced at the climacteric-like peak of the detached leaves. LPE-treated leaflets had a higher chlorophyll content and fresh weight and lower electrolyte leakage than the control. LPE-treated fruits had lower rates of ethylene and CO₂ production than did the control. LPE-treated fruits also had higher pericarp firmness and lower electrolyte leakage than the control. The results of the present study provide evidence that LPE is able to retard senescence of attached leaves and detached leaves and tomato fruits. Several recent studies suggest that lysolipids can act in a specific manner as metabolic regulators. Our results suggest a specific role of lysolipid LPE in aging and senescence     

Short period leaf movements in Oxalis regnellii

Oxalis regnellii Mig. is a trifoliate plant, and the three leaflets usually show synchronized up and down movements with a circadian period of 26–27 h. The three leaflets can also perform desynchronized ultradian oscillations, and we report on such rhythms under different conditions. A study of the occurrence of ultradian leaf movement rhythms as a function of irradiance is presented. At an irradiance of approximately 1 μW cm⁻², the occurrence was maximal and ca 30%. The periods varied from 5 to 15 h. Four other cases of ultradian rhythms in different conditions are also presented. In one case spontaneous ultradian rhythms occurred, and in another, two of the leaflets showed ultradian rhythms when the third leaflet had received a light pulse. In two more cases, the three leaflets on a leaf were separated by physical cuts along the petiole between the pulvini; in both cases the period was approximately 5 h. Possible mechanisms to explain the ultradian rhythms in Oxalis regnelli are discussed.     

Heterogeneity of soil and soil solution chemistry under Norway spruce (Picea abies Karst.) and European beech (Fagus silvatica L.) as influenced by distance from the stem basis

The present study aims at characterizing plant water status under field conditions on a daily basis, in order to improve operational predictions of plant water stress. Ohm's law analog serves as a basis for establishing daily soil-plant relationships, using experimental data from a water-limited soybean crop: 227-1. The daily transpiration flux, T, is estimated from experimental evapotranspiration data and simulated soil evaporation values. The difference, 227-2, named the effective potential gradient, is derived from i) the midday leaf potential of the uppermost expanded leaves and ii) an effective soil potential accounting for soil potential profile and an effectiveness factor of roots competing for water uptake. This factor is experimentally estimated from field observation of roots. G is an apparent hydraulic conductance of water flow from the soil to the leaves. The value of the lower potential limit for water extraction, required to assess the effective soil potential, is calculated with respect to the plant using the predawn leaf potential. It is found to be equal to –1.2 MPa. It appears that over the range of soil and climatic conditions experienced, the daily effective potential gradient remains constant (1.2 MPa), implying that, on a daily basis, transpiration only depends on the hydraulic conductance. The authors explain this behaviour by diurnal variation of osmotic potential, relying on Morgan's theory (1984). Possible generalization of the results to other crop species is suggested, providing a framework for reasoning plant water behaviour at a daily time step.     

DRIS evaluation of persimmon (Diospyrus kaki L.)

The leaf macroelement profile of fruiting shoots of persimmon was characterized by a modified diagnostic and recommendation integrated system (DRIS), using SLW as a primary determinant of leaf mineral content. Leaf N, P, Ca, and Mg content was positively and linearly correlated with SLW when expressed on leaf area basis (g mm^–2). Potassium had a negative and higher correlation to SLW when expressed on %DW basis. Mineral ratios relevant for the DRIS analysis were calculated using all four possible combinations of Area (A) and Weight (W) expressions (A/A, A/W, W/A and W/W) and correlated with leaf SLW. The particular expressions chosen for the DRIS analysis were based on their highest correlation to SLW and included N/K, P/K and Ca/Mg, based on the A/W expression of the respective nutrients and the reciprocal expression (W/A) for all other ratios. Derivation of DRIS norms were based on the mineral profile of highly exposed shoots (SLW of 15.0±0.3 mg cm^–2). Calculated indices of gradually less exposed shoots (SLW of 3.8–18.9 mg cm^–2) revealed a strong exponential imbalance of N, K and P (increasingly positive) vs Ca and Mg (increasingly negative). The calculated Nutritional Imbalance Index (NII) value of leaves decreased exponentially as shoot leaf SLW decreased. The modified DRIS analysis detected successfully a distinct mineral profile of highly vigorous fruiting water shoots, as compared to regular fruiting shoots of comparable SLW.     

Fluorescence and reflectance characteristics of manganese deficient soybean leaves: Effects of leaf age and choice of leaflet

Leaf reflectance and fluorescence characteristics of soybean (Glycine max cv Bragg) are influenced strongly by Mn availability. This report evaluates the effects of leaflet choice, leaf age, and leaf nodal position on several spectral characteristics. Leaves were obtained from soybeans grown hydroponically under controlled environmental conditions with wide differences in Mn supply. The ratio of constant yield fluorescence (F_o) to variable yield fluorescence (F_v), the ratios of reflectance at 750 nm to 550 nm and that at 650 nm to 550 nm, the position of the "red edge" near 700 nm, and an index of leaf "yellowness" were measured periodically. Increasing leaf age caused increases in the "red edge" and in both reflectance ratios. Leaf "yellowness" and the fluorescence ratio F_o/F_v decreased with leaf age and increased with leaf nodal position, primarily in Mn deficient leaves. Effects arising from leaf choice were smaller than those caused by Mn deficiency.     

Leaf responses to soil water deficits: Comparative sensitivity of leaf expansion rate and leaf conductance in field-grown sunflower (Helianthus annuus L.)

The relative importance of changes in leaf expansion rate (LER) and leaf conductance (g₁) in the control of crop transpiration depends primarily on their sensitivity to soil water deficits. The aim of this paper was to quantify the responses of LER and g₁ to soil water deficits in sunflower (Helianthus annuus L.) under conditions of moderate (spring) and high (summer) evaporative demand. Soil water content, g₁, and LER were measured in dryland (DRY) and daily-irrigated (WET) crops established on a deep sandy-loam (Typic Xerofluvent) in a Mediterranean environment. There was no difference between g₁ of DRY and WET plants (p>0.20) in contrast with a highly significant difference in LER (p<0.001). Even under the harsh conditions of the summer experiment, g₁ did not respond to water deficit in a ten-day period in which LER of DRY plants was reduced to approx. 30% of that measured in WET controls. This field study indicates that g₁ plays at most a minor role in the control of sunflower transpiration in the pre-anthesis period and confirms the importance of leaf expansion in the regulation of gas exchange of expanding canopies subjected to soil water deficits.     

Plant regeneration via somatic embryogenesis in ginger

Embryogenic callus cultures of ginger were induced from young leaf segments taken from in vitro shoot cultures. Among the four auxins tested in Murashige & Skoog medium, dicamba at 2.7 M was most effective in inducing and maintaining embryogenic cultures. Efficient plant regeneration was achieved when embryogenic cultures were transferred to Murashige & Skoog medium containing 8.9 M benzyladenine. Histological studies revealed various stages of somatic embryogenesis characteristic of the monocot system. The in vitro-raised plants have been established in soil.Abbreviations BA benzyladenine - 2,4-d 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - MS Murashige and Skoog - NAA naphthaleneacetic acid     

渍水对冬小麦生长的危害及其生理效应

小麦受渍后叶片的光合和蒸腾速率迅速下降,而后则显微弱的回升趋势。渍害不仅削弱小麦光合产物的积累,并且改变光合产物在地上部分和根系中的分配比例;植株根／冠比下降,而黄叶的发展与根／冠比的变化呈显著负相关;渍害改变小麦的发育进程,尤其是后期渍害明显促使小麦早衰。认为清水使叶片光合速率降低、光合有效面积损失和衰老加速,从而危害小麦的生长。