Liela figleaf3/5/2023 ![]() ![]() It has previously been shown that hydraulic conductance in bur oak leaves (Quercus macrocarpa Michx.), measured with the high pressure flow meter technique (HPFM), can significantly increase within 30 min following exposure to high irradiance. Underlining these results, when high irradiance levels were further used to induce elevated transpiration, the permeability of the cell membranes did not change and was imperfectly compensated by a higher increase of water transport over the apoplastic pathway (Lee et al. To illustrate this, in figleaf gourd (Cucurbita ficifolia) plants, when a cell pressure probe was used to gauge membrane permeability, low root temperature strongly reduced the hydraulic conductivity of root cortical cells and cotyledon midrib cells (Lee et al. Indeed, as also discussed by Wang and Hoch in this issue, although water is certainly slightly more viscous at positive temperatures nearing zero, its effect does not account for such large differences and much of the change in hydraulic conductivity in roots appears to be tied to changes in membrane water permeability that is mediated by aquaporins-small intrinsic membrane proteins that can act as water channels (Ionenko et al. The importance of water transport regulation by transpiration affecting the hydraulic conductivity of the roots is discussed. Measurement of E indicated that the increased water demand by the transpiring plants was fulfilled by an increase in the apoplastic pathway as principal water flow route. LRT combined with high irradiance triggered a drastic 10-fold reduction in water permeability of cortical and midrib cells and increased epsilon and T(w)(1/2) values. When the exposure of cotyledons to light was accompanied by LRT, however, ABA proved ineffective in reversing the inhibition of Lp. ![]() ![]() Midrib cells required higher concentrations of ABA (2 microM) in order to prevent the reduction in Lp(c). The reductions of Lp as the result of respective light and LRT treatments were prevented by the application of 1 microM ABA. Low root temperature (LRT) further reduced Lp(c) and E, whether it was measured under low or high irradiance levels. The exposure of cotyledons to supplemental light at warm root temperatures, however, resulted in a two- to three-fold increase in T(w)(1/2) values accompanied with the reduced hydraulic conductivity in both root cortical (Lp) and cotyledon midrib cells (Lp(c)). When exposed to low irradiance, all the water relation parameters of cortical cells remained similar at both root temperatures. The seedlings were exposed to low ambient (approximately 10 micromol m(-2) s(-1)) or high supplemental irradiance (approximately 300 micromol m(-2) s(-1) PPF density) at low (8 degrees C) or warm (22 degrees C) root temperatures. Transpiration rates (E) of cotyledons were also measured using a steady-state porometer. Water relation parameters including elastic modulus (epsilon), half-times of water exchange (T(w)(1/2)), hydraulic conductivity and turgor pressure (P) were measured in individual root cortical and cotyledon midrib cells in intact figleaf gourd (Cucurbita ficifolia) seedlings, using a cell pressure probe. ![]()
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