The effect of light and dark periods on the production of ethylene from water-stressed wheat leaves

Light was found to inhibit substantially (i.e. up to 88%) the production of ethylene induced by water stress in excised wheat leaves and from the shoots of intact plants. The relatively small amounts of ethylene emanating fron non-stressed leaves were also inhibited by light but to a smaller degree (i.e. up to 61%). In water-stressed leaves the degree of light inhibition of ethylene production was shown to be related to the age of the leaves; the amounts of ethylene diffusing from young leaves (i.e. 6-days old) was inhibited 52% by light whereas in older leaves (i.e. 9-days old) it was inhibited by 85%. Previous studies [Wright (1979) Planta 144, 179–188 and (1980) Planta 148, 381–388] had shown that application of 6-benzyladenine (BA) to leaves a day before wilting, greatly increases the amount of ethylene diffusing from the leaves following wilting (e.g. 8-fold), and to smaller degrees do applications of indole-3-acetic acid (IAA) and gibberellic acid (GA₃). On the other hand abscisic acid (ABA) treatment reduces the amount of ethylene produced. In these earlier experiments the ethylene was collected from leaves held under dark or near-dark conditions, so in the present study the activities of these growth regulators (10^-4 mol l^-1 solutions) under dark and light conditions were compared. It was found that they maintained the same relative activities on ethylene emanation (i.e. BA>IAA>GA₃>water controls>ABA) under both light and dark conditions. However, because of the inhibitory effect of light, the absolute amounts of ethylene produced from all treatments were always much higher in the dark than in the light (usually about a 6-fold difference). An interesting effect of light treatment on ethylene biosynthesis was found when water-stressed leaves were kept in dark chambers for 41/2 h and then transferred to light. Quite unexpectedly, instead of the rate of ethylene production falling immediately, it continued to be produced at the dark rate (i.e. no light inhibition!) for over 2 h before the rate began to decline, and for a much longer period (i.e. in excess of 41/2 h) if the leaves had previously been sprayed with BA. Predictably, leaves placed in the light (i.e. in leaf chambers) and then transferred to darkness, immediately or very soon produced ethylene at the dark rate. One explanation of these results, which is discussed, would be that the biosynthesis of an ethylene precursor requires an obligatory dark stage. The possible implications of these studies to a survival role of ethylene in plants during periods of water stress is discussed.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - BA 6-benzyladenine - GA₃ gibberellic acid - GLC gas-liquid chromatography - IAA indole-3-acetic acid - TLC thin-layer chromatography - _leaf leaf water potential     

Turgor pressure and water transport properties of suspension-cultured cells of Chenopodium rubrum L.

The turgor pressure and water relation parameters were determined in single photoautotrophically grown suspension cells and in individual cells of intact leaves of Chenopodium rubrum using the miniaturized pressure probe. The stationary turgor pressure in suspension-cultured cells was in the range of betwen 3 and 5 bar. From the turgor pressure relaxation process, induced either hydrostatically (by means of the pressure probe) or osmotically, the halftime of water exchange was estimated to be 20±10 s. No polarity was observed for both ex- and endosmotic water flow. The volumetric elastic modulus, , determined from measurements of turgor pressure changes, and the corresponding changes in the fractional cell volume was determined to be in the range of between 20 and 50 bar. increases with increasing turgor pressure as observed for other higher plant and algal cells. The hydraulic conductivity, Lp, is calculated to be about 0,5–2·10^–6 cm s^–1 bar^–1. Similar results were obtained for individual leaf cells of Ch. rubrum. Suspension cells immobilized in a cross-linked matrix of alginate (6 to 8% w/w) revealed the same values for the half-time of water exchange and for the hydraulic conductivity, Lp, provided that the turgor pressure relaxation process was generated hydrostatically by means of the pressure probe. Thus, it can be concluded that the unstirred layer from the immobilized matrix has no effect on the calculation of Lp from the turgor pressure relaxation process, using the water transport equation derived for a single cell surrounded by a large external volume. By analogy, this also holds true for Lp-values derived from turgor pressure changes generated by the pressure probe in a single cell within the leaf tissue. The fair similarity between the Lp-values measured in mesophyll cells in situ and mesophyll-like suspension cells suggests that the water transport relations of a cell within a leaf are not fundamentally different from those measured in a single cell.     

The maximum leaf surface temperatures of the higher plants observed in the Inland Sea area

The maximum leaf surface temperatures (MLSTs) of 126 species of higher plants were measured by means of an infrared thermometer, in the Inland Sea area, southwest of Honshu-Island, Japan, where plants suffered from severe environmental conditions due to an abnormally small amount of precipitation during the summer of 1978. The MLSTs of plants in the summer of 1978 were greater than or equal to those of 1979, when the environmental conditions were not so severe. The MLST measured in this study was 50.4 C for a non-succulent plant (Liriodendron), and 53.1 C for a succulent plant (Agave). Plants with different life forms appeared to have different MLSTs. The average of the MLSTs of conifers deciduous trees, and evergreens were 36.4, 37.7, and 40.3 C, respectively. This order corresponds to the distribution of forests from high to low, latitudes. Also the MLSTs were higher for woody plants than for herbaceous plants. Relatively high leaf temperatures were observed for climbing plants, both herbaceous and woody. Plants with narrow leaves had lower leaf surface temperatures than those with borad leaves. Herbaceous dicotyledonous plants actively growing at the end of the summer of 1978, in full sun at Hiroshima Castle were exclusively those with relatively high leaf temperatures.     

Effect of inhibitors and uncouplers on light-induced potential changes triggering photophobic responses

Light-energy absorption by Microcystis aeruginosa with and without gas vacuoles was observed, respectively by using an integrating sphere photometer. As far as the concentration of cell suspension of the order of 10⁶⁷ cells/ml in this work was concerned, the performance of gas vacuoles to shield incident light was most unlikely. Referring to a correlation secured by the integrating sphere photometer between light absorption and cell concentration of the suspension, a turbidostat culture of the blue-green alga demonstrated that the growth efficiency, Y _kJ defined as g cells harvested per kJ of light energy absorbed by the cells was nearly 0.004. This value of Y _kJ was almost the same as that of Spirulina platensis.Abbreviation vvm volume of air per volume of medium per min     

Syphacia muris: Water permeability of eggs and its effect on hatching

As a result of a previous study, it appeared that hatching of eggs of Syphacia muris is activated by the application of heat (37 °C) or cysteine or trypsin but that these are not the essential stimuli. In the present study it has been established that exposure of eggs prior to hatching for several hours to 37 °C or cysteine or trypsin, or for 3 days to 22 °C, accelerated hatching. Pretreatment with 37 °C or cysteine or trypsin also increased permeability of the eggshell to water; however, it did not induce the operculum to open. The operculum opened only if the eggs, after pretreatment, were immersed in water. The larvae could leave the opened eggs only in water and not in any other medium such as paraffin oil. These data made it possible to distinguish between three stages in the hatching process. During Stage 1, the eggshell becomes permeable to water. This can be induced by dissolving the proteins of the eggshell in a trypsin solution or by stimulating the larvae with temperature or cysteine. The permeability of the eggshell is essential to successful hatching. In Stage 2, which occurs only in the presence of water, the larvae dissolve the chitinous seal between the operculum and the eggshell. In Stage 3 the larvae probably increase their size by water absorption and leave the eggs. In the discussion it has been proposed that all nematodes, both those hatching in the intestine and the species hatching in the open, could well have an identical hatching mechanism to the one observed in Syphacia muris.     

调蓄河湖群菹草(Potamogeton crispus L.)功能性状特征及其与环境因子的关系

调水工程引起的多环境因子关联变化对沉水植物群落的影响机制有待深入探讨。以南水北调东线工程调蓄河湖群中菹草种群为研究对象,分析了京杭运河(YH)、高邮湖(GY)、洪泽湖(HZ)、骆马湖(LM)、南四湖上级湖(NS1)、南四湖下级湖(NS2)和东平湖(DP)7个调蓄河湖中菹草个体功能性状特征及其与环境因子间的关系。结果表明:(1)除高锰酸盐指数(COD_(Mn))、浊度(Tur)和底泥有机质含量(S_o)外,总氮(TN)、硝氮(NO_3-N)、氨氮(NH_4-N)、总磷(TP)、正磷酸盐(PO_4-P)、硅酸盐(SiO_4-Si)、叶绿素a(Chla)、总溶解性固体(TDS)、透明度(SD)、消光系数(K)、水温(T)、电导率(Cond)、酸碱度(pH)、溶解氧(DO)和底泥含水率(S_w)在河湖间差异达到了极显著水平;(2)菹草株高、茎分支数、茎节数、茎节长、茎直径、相对茎长、叶片数、叶厚、叶长、叶宽、叶面积、比叶面积、株重、茎重、叶重、茎叶比、茎干物质比、叶干物质比在河湖间差异极显著;(3)河湖群内菹草种群18个功能性状中,按变异系数从小到大依次为:叶宽、茎直径、叶长、茎干物质比、叶干物质比、叶面积、株高、茎节长、相对茎长、茎叶比、叶厚、茎节数、茎重、叶片数、株重、比叶面积、叶重、茎分支数;7个调蓄河湖间,按照所有性状变异系数平均值从大到小排序依次为:南四湖下级湖、洪泽湖和京杭运河、高邮湖、东平湖、南四湖上级湖、骆马湖;(4)环境因子共解释了功能性状方差变异的49.43%;叶性状主要受营养因子(TN、NO_3-N、SiO_4-Si)影响;茎性状与光照因子(Chla和SD)密切相关;底泥因子(S_o)对茎叶生物量分配起主要作用。     

供水及间甲酚对小麦间作蚕豆土壤微生物多样性和酶活性的影响

通过盆栽试验,探讨供水(田间持水量的45%、60%和75%)和化感物质间甲酚对小麦、蚕豆不同种植模式生长盛期土壤微生物多样性和酶活性的影响.结果表明,随灌水水平的降低,不同处理的土壤细菌、真菌和放线菌数量随之减少,间甲酚可加剧灌水减少引起的微生物数量的减少;间甲酚对不同处理土壤微生物多样性指数均具有降低作用,提高灌水水平可缓解间甲酚对间作群体土壤微生物多样性的负效应,但间甲酚在75%灌水水平下对单作微生物多样性的负效应最大,45%的供水水平和间甲酚作用下间作可维持更高的土壤微生物多样性.间甲酚对土壤过氧化氢酶的化感作用不显著,对脲酶和酸性磷酸酶活性的化感作用显著;3种土壤酶活性随供水水平的降低均显著下降,但供水与间甲酚、种植模式的互作效应对酶活性的影响不显著;间作对土壤过氧化氢酶和酸性磷酸酶活性具有极显著影响.