An endogenous circadian rhythm of transpiration in Tamarix aphylla

Abstract

An endogenous circadian rhythm in the transpiration of Tamarix aphylla (L.) Karst. was found for plants grown in continuous light under laboratory conditions. The mean period (±SD) was 21.7±2.3 h (n = 121). No such rhythm was observed in continuous darkness, except for one small hump at the time of the first cycle. The influence of NaCl, Cd(NO3)2 and LiCi on the rhythmic behaviour of young T. aphylla plants was investigated. NaCl concentrations of up to 150 mM reduced the overall transpiration rates of the plants, but did not change the period of the rhythm. The amplitude and the mesor of the oscillations were inversely correlated with the NaCl concentration. A similar influence was found for Cd(NO3)2, but with concentrations that were approximately three orders of magnitude smaller than those of the NaCl treatments. The rhythmic behaviour of the plants was not altered by 10 mM LiCl. It is suggested that the described rhythm of transpiration may have a dual effect: (a) it might cause a partial closure of the stomates during midday hours and (b) it might serve as a possible synchronizer (“master clock”) for other rhythmic phenomena in the plants.

Excretion of ions (Cd2+, Li+, Na+ and Cl−) by Tamarix aphylla

“…1). Thus, the Cd-* tolerance of T. aphylla (Hagemeyer and Waisel 1987) must be related to other mechanisms than ioti excretion. For example, tolerance might involve chemical immobilization as was shown for other plant species (Casterlinc and Barnctt 1982, Rauser ct al.…”

“…Plants with a rapid mineral turnover seem to be capable of coping not only with NaCl, but also with an excess of other elements. In preliminary experiments, it was shown that T. aphylla survives comparatively high concentrations of Cd-* and Li* (Hagemeyer and Waisel 1987). Thus, the response of f. aphylla to high concentrations of Cd-* as well as to LiCl and NaCl has now been further investigated.…”

Rhythms in Plants

“…10 mM LiCl given to intact Tamarix plants caused no lengthening in the circadian transpiration rhythm (Hagemeyer and Waisel 1987), although lithium slows down circadian rhythms in general, acts on aquaporins in renal functions (Nielsen et al 2002), and has a broad spectrum of action mechanisms. It might be that the ion could not enter the leaves in the Tamarix case (cf.…”

“…7.5.1), i.e., rhythmic endogenous transpiration with a period close to but not exactly 24 h. An example is the transpiration rhythm in the tree Tamarix aphylla (L.) Karst. with a mean period of around 22 h in light (Hagemeyer and Waisel 1987). The rhythmic transpiration can be entrained to-"locked to" or "in phase with"-external rhythmic signals, e.g., light signals.…”

“…2 in Webb 1998). The tree Tamarix aphylla (L.) showed a circadian transpiration rhythm in light with period about 22 h (Hagemeyer and Waisel 1987). Brinker et al (2001) indicate that stomatal aperture was under circadian control in the gymnosperm Ginkgo biloba.…”