Decline in stomatal response to leaf water deficit in Corylus maxima cuttings.

Many woody species can be propagated from leafy cuttings. However, following rooting, cuttings of Corylus maxima Mill. cv. Purpurea do not always survive the transition from a highly supportive rooting environment (e.g., fog) to a more natural environment where evaporative demand is higher. We found that it is not the supply of water to leaves, but stomatal dysfunction that leads to severe water deficits in the rooted cuttings. Two hours after well-rooted cuttings were transferred from the rooting environment, we were able to relate visible signs of leaf water deficit to high stomatal conductance (g(s)) and low relative water content (R). Small expanding leaves (L3) had unusually high g(s) and lower R than fully expanded leaves (L1). Although high cuticular conductances (g(c)) were occasionally observed in L3, SEM confirmed that increased total leaf conductance (g) was mainly a result of abnormally wide stomatal opening. We measured changes in the ability of stomata to control water loss during rooting by determining stomatal responsiveness to leaf water deficit in detached L1 and L3 harvested from cuttings during the first 75 days after severance from stock plants. Reduced stomatal responsiveness was observed within 7 days of severance, prior to adventitious root formation, and was more pronounced in L3 than in L1. A period of acclimatization after rooting (no leaf wetting, but a vapor pressure deficit of 0.20 kPa) reduced g(s) by 50% in L3 but not in L1, and partially restored stomatal responsiveness in L1 but not in L3. After rooting, the original leaves on the cutting retained substantial capacity for photosynthesis (e.g., in L1, 8 micromol m(-2) s(-1) at a photosynthetic photon flux density of 400 micromol m(-2) s(-1)). The implications of the results for post-rooting acclimatization procedures are discussed.

Relationships between structural development and the absorption of ions by the root system of Cucurbita pepo.

In both the seminal axis and lateral roots of Cucurbita pepo L. the formation of large central xylem elements and the commencement of secondary cambial activity occur 10-20 cm from the root tip. Concomitant with or slightly preceding these developments there are changes in the structure of the walls of endodermal cells where the lignified casparian band spreads along the radial wall and substances staining with Sudan IV are deposited in both radial and tangential walls. At distances more than 30 cm from the tip of primary roots the radius of the stele increases considerably causing splits in the cortex. The endodermis is stretched and the suberin becomes organized in a lamellar form.Against this background of anatomical change certain of the transport capabilities of the root are retained while others are lost. Using an apparatus for measuring the uptake of tracers by segments of intact roots it was found that neither the uptake nor translocation of potassium seem to be affected by the suberization of the endodermis or by secondary thickening, while the translocation of calcium is virtually eliminated when these processes begin. As the root ages its ability to absorb phosphate declines although the translocation of the phosphate absorbed is much less affected by structural development than that of calcium.The observed rates of potassium uptake by complete root systems could be predicted quite accurately from the average of segment uptake data suggesting that the method used gives reliable results.