The ability of stems of Laurus nobilis (L.) to refill embolised xylem conduits was studied in plants both at optimal water supply (W) and under conditions of soil drought inducing xylem pressures (Px) of -1.54 (S1) and -2.35 MPa (S2). Starch depolymerisation in wood parenchyma was measured as percentage of cells 'with high starch content' (HSC-cells) counted under a microscope. HSC-cells decreased during embolism and increased again in refilled stems. A direct relationship was found between percentage of HSC-cells and Px, with HSC-cells between 65 and 75% of the total at Px ≥ -0.6 MPa, at which recovery from PLC was recorded. At low transpiration, starch re-appeared in wood parenchyma cells but only in plants that showed diurnal stomatal opening (W- and S1-plants). In S2-plants showing diurnal stomatal closure and nocturnal opening with Px between -1.2 to -2.4 MPa, HSC-cells were only 25% and plants did not recover from PLC. This finding suggests that (i) the Px threshold for embolism repair was ≥ -0.6 MPa, and (ii) impeded phloem loading limits starch content in wood parenchyma and embolism repair. We conclude that starch depolymerisation acts as a signal to phloem unloading sugars to embolised conduits thus generating the necessary osmotic gradients driving refilling.

译文

:在最佳供水(W)以及土壤干旱导致木质部压力(Px)为-1.54(S1)和-2.35的条件下,研究了月桂(L.)茎在重新栓塞木质部导管时的能力。 MPa(S2)。木材薄壁组织中的淀粉解聚以显微镜下计数的“具有高淀粉含量”的细胞(HSC细胞)的百分比进行测量。 HSC细胞在栓塞过程中减少,并在重新填充的茎中再次增加。发现HSC细胞的百分比与Px之间存在直接关系,在Px≥≥-0.6MPa时,HSC细胞占总数的65%至75%,并记录了从PLC恢复的情况。在低蒸腾作用下,淀粉重新出现在木实质细胞中,但仅在表现出昼夜气孔开口的植物(W和S1植物)中重新出现。在表现出昼夜气孔关闭和夜间开放且Px在-1.2至-2.4 MPa之间的S2植物中,HSC细胞仅占25%,植物没有从PLC恢复。这一发现表明:(i)栓塞修复的Px阈值≥≥-0.6MPa,(ii)韧皮部负荷受限限制了木材薄壁组织和栓塞修复中的淀粉含量。我们得出的结论是,淀粉解聚反应是韧皮部将糖卸载到栓塞导管中的信号,从而产生了驱动充填的必要渗透梯度。

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