Localization of Mechanisms Involved in Hydropassive and Hydroactive Stomatal Responses of Sambucus nigra to Dry Air

Abstract

The response of stomata to a reduction of air humidity is composed of a hydropassive opening followed by active closure. Whereas the mechanisms behind the hydropassive opening are largely understood, the location and physiological basis of the sensing mechanisms leading to active closure are not yet known. This study attempts to evaluate the importance of a single pore's transpiration on its own response and that of adjacent pores. Selected stomata on attached intact leaves of Sambucus nigra were sealed with mineral oil and the response to a reduction of humidity was continuously observed in situ. Blocking a pore's transpiration had no appreciable effect on hydropassive opening and subsequent stomatal closure. If the adjacent stomata were additionally sealed, the closing response was reduced, but not the hydropassive opening. On the other hand, sealing the entire leaf surface, except a small area including the observed stomata, also reduced stomatal closure. These results indicate that strictly local processes triggered by a pore's own transpiration are not required to induce stomatal closure. To describe the effect of one pore's transpiration on the hydropassive and hydroactive responses of neighboring stomata, a simple spatial model was constructed. It suggests that 90% of the closing effect covers an area of approximately 0.5 mm 2 , whereas the effect on hydropassive opening affects an area of approximately 1 mm 2 . This divergence may suggest mechanisms other than or in addition to those involving changes of local leaf water potential.

Signal coordination before, during and after stomatal closure in response to drought stress

“…Similar to previous experiments, it was found that the first registered response in stomatal conductance to drought stress initiation in both dry‐down treatments was a short‐lived sudden increase (Wrong Way or Iwanoff effect) followed by a continual decline as drought conditions persisted (Iwanoff, ; Paoletti, ; Kaiser & Grams, ; Kaiser & Legner, ; Powles et al ., ; Hoshika et al ., ; Kaiser & Paoletti, ) (Figs , ). Moreover, changes in surface potentials and the peak of stem and petiole AE events were concurrent with the time at which stomatal conductance (gs) peaked (I2 gs ), also demonstrating a close correlation with stomatal closure (Fig.…”

Leaf structural changes associated with iron deficiency chlorosis in field-grown pear and peach: physiological implications

“…Leaf weight was monitored for 4 days and water loss was expressed as a percentage of the initial FW was found to occur in chlorotic leaves. After interrupting xylem water supply to the leaf, stomatal opening could be explained by a rapid loss of turgor pressure, either of the surrounding epidermal cells (Raschke 1970a, b) or both the epidermal and guard cells (Kaiser and Legner 2007). The mechanical advantage of epidermal cells over guard cells (DeMichele and Sharpe 1973) results in a hydropassive stomatal opening phase, followed by an active stomatal closure phase.…”

The contributions of apoplastic, symplastic and gas phase pathways for water transport outside the bundle sheath in leaves

“…; Scoffoni et al . ), patterns of isotopic enrichment (Barbour & Farquhar ) and stomatal behaviour (Buckley ; Kaiser & Legner ; Peak & Mott ). The overarching goal of the present study was to place hypotheses about restrictions on leaf water flow outside the xylem on an explicitly anatomical and biophysical basis.…”