压力室测定根系导水率方法探讨

用压力室连续测定了玉米根系长压和降压过程的导水率,结果表明,降压过程湍 得的根系导水率显著大于用升压过程的,并且前者的相关系数大于后者,这种差异是由于这两个过程中质外体途径细胞壁空间充水量不同造成的,开始升压时,由于细胞壁空间含水量低,质外体途径阻力大,导致非结构阻力;随着压力的升高,细胞壁空间含水量增大,质外体途径导度增大,减小甚至可以消除非结构阻力,降压法可以使根系快速复水,消除传统方法因长时间复水所致根结构的改变。建议用降压法测定根系导水率。     

两种苹果砧木根系水力结构及其PV曲线水分参数对干旱胁迫的响应

研究干旱胁迫对平邑甜茶(Malus hupehensis)和楸子(Malus prunifolia)根系水力结构及其PV曲线水分参数的影响.设定正常与干旱2种水分处理,对2种苹果砧木进行氯化汞-巯基乙醇处理和压力室-容积(PV)曲线测定试验,并利用高压流速仪(HPFM),测定平邑甜茶和楸子根系水力结构.结果表明:随着水分胁迫的加重,平邑甜茶和楸子的根系导水率、根系叶比导水率、根系茎比导水率出现减少趋势.在适宜水分和重度干旱条件下,平邑甜茶根系叶比导水率分别为楸子根系叶比导水率的95％和92％,平邑甜茶根系茎比导水率分别为楸子根系茎比导水率的52％和62％,楸子与平邑甜茶相比在根系茎比导水率和根系叶比导水率上出现增加趋势.干旱胁迫可能会导致水通道蛋白的活性受到抑制,致使其根系导水率出现降低,继而导致了地上部分气体交换受到影响.严重干旱时,楸子与平邑甜茶相比可能具有更大的水孔蛋白表达量来抵御干旱胁迫.在2种水分条件下,楸子的初始质壁分离时的渗透势(ψstlp)、饱和含水时的渗透势(Ψssal)、初始质壁分离时的相对水含量(RWCtlp)、初始质壁分离时的相对渗透水含量(ROWCtlp)、组织细胞总体弹性模量(ε')值与平邑甜茶相比较均处于较低水平,束缚水含量(Va)值处在较高水平.对PV曲线水分参数进行隶属函数综合评价得出的△值为楸子大于平邑甜茶,平邑甜茶和楸子之间b值差异不明显.在适宜水分和重度干旱条件下楸子所体现出的输水策略优于平邑甜茶.PV曲线水分参数同苹果砧木根系的水力结构一样能够随着植物所处的环境做出相应的调整.对于PV曲线水分参数研究发现,楸子在膨压保持方面与平邑甜茶相比,其抗旱性优于平邑甜茶.     

Cr6+胁迫对小麦幼苗根系生长的影响及DNA损伤效应研究

研究了Cr6+胁迫对3 d和10 d龄小麦幼苗根系生长的影响及DNA损伤效应.结果表明(1)>5 mg/L的Cr6+均显著或极显著降低幼苗根长、根数及根系鲜重、干重,3 d龄幼苗根系生长比10 d龄幼苗对Cr6+胁迫更敏感;(2)所试浓度Cr6+均降低两苗龄幼苗根系DNA含量;5～20 mg/L Cr6+浓度范围内,3 d龄幼苗根系DNA含量下降幅度大于10 d龄幼苗,Cr6+浓度>20 mg/L时,3 d龄幼苗根系DNA含量低于10 d龄幼苗;(3)Cr6+对两苗龄幼苗根系DNA增色效应的影响均呈现随浓度增大先升高后下降的趋势;3 d龄幼苗根系DNA增色效应在5～60 mg/L Cr6+浓度范围内大于对照,Cr6+浓度>60 mg/L时则小于对照;在所试Cr6+浓度范围内,10 d龄幼苗根系DNA增色效应均大于对照.     

根径向水流导度测定技术的改进

根系径向流的水力学性质主要是根的径向水流导度,它取决于径向水流通道的状况。利用改进的现有原位的测定根系径向水流导度的蒸腾计技术,设计了一个简便的４室吸水测定装置,可一次性获得根本质部水势和根径向水流导度,缩短测定时间１０ｍｉｎ,确保测定精度。然后用改进的装置测定了生长在不同水分条件下冬小麦（Ｔｒｉｔｉｃｕｍ ａｅｓｔｉｖｕｍＬ．）根系的径向水流导度,结果显示根系的平均径向水流导度为４．６３＊１０＾     

植物钙素吸收和运转

近年来,钙素在植物体内的吸收和运输研究主要集中在细胞和分子水平,但整株水平上的研究也同样重要.整株水平上的钙吸收和运输包括根细胞的钙吸收、钙离子横向穿过根系并进入木质部、在木质部运输、从木质部移出并进入叶片或果实及在叶片或果实中运转分配等环节,既经过质外体也穿越共质体.钙离子通道、Ca2 -ATP酶和Ca2 /H 反向转运器等参与根细胞的钙吸收.在钙离子横向穿根进入木质部的过程中,需要穿越内皮层和木质部薄壁细胞组织.根系内皮层凯氏带阻挡了Ca2 沿质外体途径由内皮层外侧向内侧的移动,部分Ca2 由此通过离子通道流进内皮层细胞而转入共质体并到达木质部薄壁细胞组织,而由木质部薄壁细胞组织进入中柱质外体可能需要Ca2 -ATP酶驱动;还有一些Ca2 由内皮层细胞运出,沿内皮层内侧的质外体途径进入木质部导管,并通过导管运向枝干.钙离子以螯合态的形式在枝干导管运输;水流速率是影响钙离子沿导管运输的关键因子.钙离子在果实和叶片中的运输和分配不仅通过质外体途径也通过共质体途径.     

杨树根压昼夜周期性及其影响因子

为研究土壤盆栽和溶液培养的‘84K’(Populus alba×P.glandulosa)离体根系的根压及根压昼夜节律,系统探讨影响根压的因素及它们与根压的关系,深入了解根压的产生机制及其节律调控,采用压力转换器法对‘84K’离体根系的根压进行了研究。该研究采用不同时间取样、摘叶、环割等试验处理,不同土壤温度、昼夜温差/恒温等测定条件研究了离体根压的节律,并进一步运用化学抑制剂研究根系呼吸代谢、根系导水率对根压的影响,并测定伤流液的渗透强度及其无机离子和可溶性糖含量日变化以探讨它们和根压昼夜节律的关系。研究发现,‘84K’离体根系的根压具有昼高夜低的周期节律,在上午至正午达到峰值,在20:00达到谷值。不同取样时间、不同培养介质对根压周期性有一定的影响,但总体昼高夜低没有改变。摘叶、环割、呼吸抑制剂或细胞膜水导抑制剂影响根压峰值的大小,但对根压的昼夜节律没有明显影响。摘叶、环割或呼吸抑制剂显著地降低了根压峰值,而水导抑制剂对根压峰值影响不大,说明根压峰值的大小主要受呼吸作用,包括呼吸底物的影响,而根系水导率对根压峰值的影响不大。根压峰值随土壤温度下降而下降、土壤温度还改变根压的昼夜节律。随温度的变化,最大根压和呼吸速率同步变化,意味着根压随温度的变化也是呼吸代谢在起作用。根系伤流液渗透强度白天高晚上低。伤流液无机离子含量以及可溶性糖含量的日变化和渗透强度变化一致,其中无机离子扮演更主要的角色。昼夜温差条件下的根压峰值显著大于昼夜常温条件下的根压峰值。总之,‘84K’根压呈现较稳定的昼夜周期性,昼高夜低。根压峰值大小主要受呼吸代谢的调控,呼吸抑制剂、呼吸代谢底物、影响呼吸作用的温度等都影响‘84K’根压峰值的大小。根系导水率对根压有一定的影响,但不显著。     

干旱胁迫下外源茉莉酸甲酯对玉米幼苗根系吸水的影响

茉莉酸类化合物作为环境信号分子,不仅参与植物生长发育的调控,同时受到环境胁迫的诱导,参与植物对逆境胁迫的响应和防御。本研究以北方广泛种植的玉米品种‘郑单958’为材料,通过对根系外源施加茉莉酸甲酯的方式,探究干旱胁迫下茉莉酸甲酯对玉米幼苗抗旱性以及根系吸水的影响。结果表明,外源茉莉酸甲酯可提高玉米幼苗光合速率、蒸腾作用和气孔导度,增强抗氧化酶活性,降低H_2O_2和丙二醛的含量,从而缓解干旱胁迫对植株造成的损伤。通过测定根系水导、氯化汞处理的蒸腾速率的变化以及水通道蛋白的表达量,发现干旱胁迫下外源茉莉酸甲酯可增强根系水通道蛋白的表达,进而增强玉米幼苗的根系吸水能力,从而缓解干旱胁迫造成的叶片水分含量的下降和水势的降低,提高了玉米幼苗的抗旱性。     

NaCl胁迫对黄瓜根系边缘细胞发生的影响

以黄瓜为试材,研究了NaCl处理对植株生物量、根长、根系活力、根边缘细胞的数目和活性及黏胶层厚度的影响。结果表明,NaCl处理降低了植株生物量与根系长度,增加了黄瓜幼苗的根系活力。黄瓜边缘细胞的出现几乎与根同时发生,当根长达到25mm时,边缘细胞的数目与活性均达到最大值。NaCl处理对边缘细胞的数目与活性表现出一定的抑制作用。离体根尖的边缘细胞活性也随NaCl处理浓度与处理时间的增加而逐渐减小,但根边缘细胞黏胶层厚度却随NaCl处理浓度的增加而增加。总之,NaCl对黄瓜幼苗造成一定伤害,但根系边缘细胞可通过降解死亡与增加黏胶的分泌量在一定程度上减轻这种伤害程度。     

植物根系吸水机理的研究进展

近年来,植物根系吸水机理在细胞、组织和整体水平上的研究进展非常迅速,对阐明植物抗旱机制及其高效利用有限水资源途径的探讨具有重要意义.本文主要对植物根的复合结构和根系在土壤中的分布、根系中水流性质等方面的最新研究状况进行了概述,特别详细地论述了水通道蛋白的表达及功能与根系中水分运动的关系、以及根系输水的调节和根系吸水过程中的信号传导方面的研究动态,并且评价了根的复合运输模型和根系吸水的数学模型等,最后就其可能生理意义及其应用前景作了评述.     

植物根系吸水机理的研究进展

近年来,植物根系吸水机理在细胞、组织和整体水平上的研究进展非常迅速,对阐明植物抗旱机制及其高效利用有限水资源途径的探讨具有重要意义。本文主要对植物根的复合结构和根系在土壤中的分布、根系中水流性质等方面的最新研究状况进行了概述,特别详细地论述了水通道蛋白的表达及功能与根系中水分运动的关系、以及根系输水的调节和根系吸水过程中的信号传导方面的研究动态,并且评价了根的复合运输模型和根系吸水的数学模型等,最后就其可能生理意义及其应用前景作了评述。     

Hydraulic conductance and mercury-sensitive water transport for roots of Opuntia acanthocarpa in relation to soil drying and rewetting

Drought-induced changes in root hydraulic conductance (LP) and mercury-sensitive water transport were examined for distal (immature) and mid-root (mature) regions of Opuntia acanthocarpa. During 45 d of soil drying, LP decreased by about 67% for distal and mid-root regions. After 8 d in rewetted soil, LP recovered to 60% of its initial value for both regions. Axial xylem hydraulic conductivity was only a minor limiter of LP. Under wet conditions, HgCl2 (50 microM), which is known to block membrane water-transport channels (aquaporins), decreased LP and the radial hydraulic conductance for the stele (L(R, S)) of the distal root region by 32% and 41%, respectively; both LP and L(R, S) recovered fully after transfer to 2-mercaptoethanol (10 mM). In contrast, HgCl2 did not inhibit LP of the mid-root region under wet conditions, although it reduced L(R, S) by 41%. Under dry conditions, neither LP nor L(R, S) of the two root regions was inhibited by HgCl2. After 8 d of rewetting, HgCl2 decreased LP and L(R, S) of the distal region by 23% and 32%, respectively, but LP and L(R, S) of the mid-root region were unaltered. Changes in putative aquaporin activity accounted for about 38% of the reduction in LP in drying soil and for 61% of its recovery for the distal region 8 d after rewetting. In the stele, changes in aquaporin activity accounted for about 74% of the variable L(R, S) during drought and after rewetting. Thus, aquaporins are important for regulating water movement for roots of O. acanthocarpa.     

Effects of Phosphorus Nutrient on the Hydraulic Conductivity of Sorghum (Sorghum vulgare Pers.) Seedling Roots Under Water Deficiency

Hydroponic experiments were conducted in a growth chamber and changes in the hydraulic conductivity of sorghum (Sorghum vulgare Pers.) roots (Lpr) at the three-leaf stage were measured using the pressure chamber method. Water deficiency was imposed with polyethylene glycol (PEG) 6000 and the phosphorus (P) levels were controlled by complete Hoagland solution with and without P nutrient. The objective of this study was to investigate the effect of P nutrition on root Lpr under water deficiency. The results showed that the Lpr in P deficiency treatments decreased markedly, but the Lpr recovered to the same value as that of control when sufficient P was supplied for 4-24 h. Water deficiency decreased Lpr, but the hydraulic conductivity of the roots with sufficient P supply was still higher than that of plants without P supply. When resuming water supply, the Lpr of the water-deficient plants under P supply recovered faster than that of plants without P supply, which indicates that plants with sufficient P nutrient are more drought tolerant and have a greater ability to recover after drought. The treatment of HgCl2 indicated that P nutrient could regulate the Lpr by affecting the activity and the expression levels of aquaporins.     

Effects of Phosphorus Nutrient on the Hydraulic Conductivity of Sorghum （Sorghum vulgare Pers.） Seedling Roots Under Water Deficiency

Hydroponic experiments were conducted in a growth chamber and changes in the hydraulic conductivity of sorghum (Sorghum vulgare Pers.) roots (Lpr) at the three-leaf stage were measured using the pressure chamber method. Water deficiency was imposed with polyethylene glycol (PEG) 6000 and the phosphorus (P) levels were controlled by complete Hoagland solution with and without P nutrient. The objective of this study was to investigate the effect of P nutrition on root Lpr under water deficiency. The results showed that the Lpr in P deficiency treatments decreased markedly, but the Lpr recovered to the same value as that of control when sufficient P was supplied for 4-24 h. Water deficiency decreased Lpr, but the hydraulic conductivity of the roots with sufficient P supply was still higher than that of plants without P supply. When resuming water supply, the Lpr of the water-deficient plants under P supply recovered faster than that of plants without P supply, which indicates that plants with sufficient P nutrient are more drought tolerant and have a greater ability to recover after drought. The treatment of HgCl2 indicated that P nutrient could regulate the Lpr by affecting the activity and the expression levels of aquaporins.     

Onion root water transport sensitive to water channel and K+ channel inhibitors

Transroot osmotic water flux (Jos) and radial hydraulic conductivity (Lpr) in onion roots were greatly increased by three means; infiltration of roots by pressurization, repetition of osmosis and chilling at 5 degrees C. Jos was strongly reduced by the water channel inhibitor HgCl2 (91%) and the K+ channel inhibitor nonyltriethylammonium (C9, 75%), which actually made the membrane potential of root cells less sensitive to K+. C9 decreased the rate of turgor reduction induced by sorbitol solution to the same extent as HgCl2. Thus, C9 is assumed to decrease the hydraulic conductivity (Lp) of the plasma membrane by blocking water channels, although possible inhibition of the plasmodesmata of the root symplast by C9 cannot be excluded. Onion roots transported water from the tip to the base in the absence of the osmotic gradient. This non-osmotic water flux (Jnos) was equivalent to Jos induced by 0.029 M sorbitol. Jnos increased when Jos was increased by repetition of osmosis and decreased when Jos was decreased by either HgCl2 or by C9. The correlation between Jnos and Jos suggests that non-osmotic water transport occurs via the same pathways as those for osmotic water transport.     

Phosphorus deficiency-induced reduction in root hydraulic conductivity in Medicago falcata is associated with ethylene production

Plants grown in phosphorus-deficient solutions often exhibit disruption of water transport due to reduction in root hydraulic conductivity (Lpr) and enhanced ethylene production. To uncover the relationship between the reduction in Lpr and increase in ethylene production, we investigated effect of phosphorus (P) deficiency on ethylene production and Lpr in legume plants of Medicago falcata L. There was an increase in ethylene production and a reduction of Lpr of M. falcata roots when M. falcata seedlings grown in P sufficient solutions (0.5 mM H₂PO₄^2?) were transferred to P-deficient solutions (5 μM H₂PO₄^2?). Antagonists of ethylene biosynthesis, CoCl₂ and aminoethoxyvinylglycine (AVG), abolished the P deficiency-induced ethylene production. Root hydraulic conductivity of M. falcata seedlings grown in P-sufficient solutions was insensitive to CoCl₂ and AVG, while the two chemicals enhanced Lpr for those grown in P-deficient solutions, suggesting that P deficiency-induced decrease in Lpr can be reversed by inhibiting ethylene production. Ethylene precursor 1-amino cyclopropane-1-carboxylic acid (ACC) and ethylene donor ethephon had greater inhibitory effect on Lpr of P-sufficient seedlings than that of P-deficient seedlings. Root hydraulic conductivity of P-sufficient seedlings was more sensitive to HgCl₂ than that of P-deficient seedlings. Taken together, these findings suggest that ethylene induced by P deficiency may play an important role in modulation of root hydraulic conductivity by affecting aquaporins in plants.     

水曲柳幼苗根系在不同浓度NH4NO3溶液中水流导度的变化

水分吸收过程是根系重要的生理过程。水孔蛋白在根系水分径向运输中起着重要的作用,根系水流导度(L_p)的测定是研究水孔蛋白的重要途径。该研究采用压力流的方法,对相同生长条件下的水曲柳(Fraxinus mandshurica)幼苗根系进行研究,测定了根系在去离子水和不同浓度NH₄NO₃溶液中的L_p。结果表明:未经处理的水曲柳幼苗根系,L_p随NH₄NO₃浓度的增加而上升,而且NH₄NO₃溶液中的L_p比去离子水中的L_p平均高77%;经HgCl₂处理后,水曲柳幼苗根系的L_p仍然随NH₄NO₃浓度的增加而增大,但是根系L_p在去离子水下降了22%,而在NH₄NO₃溶液中下降了68%,与以前的研究相比发现,经HgCl₂处理后,以营养液为吸水基质的根系L_p的降低值普遍高于以去离子水为基质的试验。因此,基质中养分离子的存在对根系中水孔蛋白活性产生了重要的影响,进而影响根系水分的吸收过程。     

Gating of aquaporins by low temperature in roots of chilling-sensitive cucumber and chilling-tolerant figleaf gourd

Effects of low temperature (8 degrees C) on the hydraulic conductivity of young roots of a chilling-sensitive (cucumber, Cucumis sativus L.) and a chilling-resistant (figleaf gourd, Cucurbita ficifolia Bouche) crop have been measured at the levels of whole root systems (root hydraulic conductivity, Lp(r)) and of individual cortical cells (cell hydraulic conductivity, Lp). Exposure of roots to low temperature (LRT) for up to 6 d caused a stronger suberization of the endodermis in cucumber compared with figleaf gourd, but no development of exodermal Casparian bands in either species. Changes in anatomy after 6 d of LRT treatment corresponded with a reduction in hydrostatic root Lp(r) of cucumber roots by a factor of 24, and by a factor of 2 in figleaf gourd. In figleaf gourd, there was a reduction only in hydrostatic Lp(r) but not in osmotic Lp(r) suggesting that the activity of water channels was not much affected by LRT treatment in this species. Changes in cell Lp in response to chilling and recovery were similar to the root levels, although they were more intense at the root level. Activation energies (E(a)) and Q10 of water flow as measured at the cell level were high in cucumber (E(a)=109+/-13 kJ mol(-1); Q(10)=4.8+/-0.7; n=6-10 cells), but small in figleaf gourd (E(a)=11+/-2 kJ mol(-1); Q10=1.2+/-0.1; n=6-10 cells). Roots of figleaf gourd recovered better from LRT treatment than those of cucumber. In figleaf gourd, recovery (at both the root and cell level) often resulted in Lp and Lp(r) values which were even bigger than the original, i.e. there was an overshoot in hydraulic conductivity. These effects were larger for osmotic (representing the cell-to-cell passage of water) than for hydrostatic Lp(r). After a short-term (1 d) exposure to 8 degrees C followed by 1 d at 20 degrees C, hydrostatic Lp(r) of cucumber nearly recovered and that of figleaf gourd still remained higher due to the overshoot. By contrast, osmotic Lp(r) and cell Lp in both species remained high by a factor of 3 compared with the control, possibly due to an increased activity of water channels. After preconditioning of roots at LRT, increased hydraulic conductivity was completely inhibited by HgCl2 at both the root and cell levels. Different from figleaf gourd, recovery from chilling was not complete in cucumber after longer exposure to LRT. It is concluded that at LRT, both changes in the activity of aquaporins (AQPs) and alterations of root anatomy determine the water uptake in both species. The high temperature dependence of cell Lp in cucumber suggests conformational changes of AQPs during LRT treatment which result in channel closure and in a strong gating of AQP activity by low temperature. This mechanism is thought to be different from that in figleaf gourd where AQPs reacted in the conventional way, i.e. low temperature affected the mobility of water molecules in AQPs rather than their open/closed state, and Q(10) was low.