Induction of Curvature in Maize Roots by Calcium or by Thigmostimulation

Abstract

We examined the response of primary roots of maize (Zea mays L. cv Merit) to unilateral application of calcium with particular attention to the site of application, the dependence on growth rate, and possible contributions of thigmotropic stimulation during application. Unilateral application of agar to the root cap induced negative curvature whether or not the agar contained calcium. This apparent thigmotropic response was enhanced by including calcium in the agar. Curvature away from objects applied unilaterally to the extreme root tip occurred both in intact and detipped roots. When agar containing calcium chloride was applied to one side of the postmitotic isodiametric growth zone (a region between the apical meristem and the elongation zone), the root curved toward the side of application. This response could not be induced by plain agar. We conclude that curvature away from calcium applied to the root tip results from a thigmotropic response to stimulation during application. In contrast, curvature toward calcium applied to the postmitotic isodiametric growth zone results from direct calcium-induced inhibition of growth. application, (c) localized changes in growth rate accompanying the curvature, and (d) the possible induction of curvature by mechanical stimulation during Ca application. MATERIALS AND METHODS Plant MaterialCaryopses of maize (Zea mays L. cv Merit; Asgrow Seeds, Vineland, NJ) were soaked in tap water overnight and planted between wet paper towels on an opaque plastic tray. A second tray was applied on top and the two trays, forming a sandwich holding the caryopses, were taped together. The trays were held vertically in a pan with the paper towels along the lower end of the tray contacting standing water in the pan. The trays were kept under fluorescent lights (Sylvania coolwhite, approximately 5 jimol m-2 s1'). Seedlings were used when the primary roots were 2 to 3 cm long (about 3 d after soaking).In earlier work, we reported that asymmetric application of Ca near the tips of primary roots of maize causes curvature toward the Ca (17). We also found that immersion of roots in Ca-containing solution causes transient inhibition of elongation (8). Based on these observations, we suggested that curvature toward Ca results from inhibition of root growth by Ca (10).Takahashi et al. (24) reported effects of Ca opposite to ours. They found that application of Ca to the cap stimulated elongation and that unilateral application induced negative curvature by accelerating elongation on the side to which Ca was applied. We also observed curvature away from Ca in some of our experiments (11).Ca has been implicated as a mediator of root gravitropism (2, .17) and may also play a role in the modification of gravitropic behavior by light (18,21,24). In view of the apparent importance of Ca in root gravitropism, we reexamined the phenomenon of Ca-induced curvature with special attention to (a) kinetics, (b) dependence on the site of l Supported by National Aeronautics and Space Administration grant N...

Cytoplasmic Free Ca2+ in Arabidopsis Roots Changes in Response to Touch but Not Gravity

“…Using Ca2+-specific microelectrodes, Bjorkman and Cleland (1991) found a distinct and differential gradient in the apoplastic Ca2+ activity between the upper and the lower side of gravistimulated maize (Zea mays L.) root tips that was required for gravitropism. These observations, in conjunction with the finding that asymmetric application of Ca2+ caused curvature toward the source (Ishikawa and Evans, 1992), provide indirect evidence that gravity-induced Ca2+ redistribution is necessary for gravitropic curvature. The development of this asymmetry in apoplastic Ca2+ may mediate growth control.…”

“…However, the evidence has been indirect and sometimes contradictory. For example, unilateral application of Ca 2+ via agar blocks, which has often been cited as evidence for a role of Ca 2 + asymmetries in the root graviresponse, do not always lead to the same result (Hasenstein et al, 1988;Ishikawa and Evans, 1992;Takahashi et al, 1992). Ca 2< transport studies have shown the preferential polar transport of 45 Ca 2 ' toward the lower side of graviresponding maize roots (Lee et al, 1983b), but no asymmetry in free Ca 2+ between upper and lower sides of the roots could be detected (Dauwalder et al, 1985).…”

“…It has been proposed that touch and gravity-related responses may be closely linked (Trewavas and Knight, 1994). Thus touching a root can elicit tropic curvature (Ishikawa and Evans, 1992) or even interrupt growth for severa1 hours (Hanson and Trewavas, 1982). Although the precise mechanism whereby touch is transduced to tropic or developmental events is unknown many studies have highlighted the role of [Ca"], in this process (for review, see Trewavas and Knight [1994]; Knight et al, 1994).…”

Specialized Zones of Development in Roots: View from the Cellular Level

“…The length of this region thus represents about 5.5% of the entire growth zone. Subsequent studies confirmed the uniqueness of the cells located in the PIG zone, not only from a morphometrical point of view, but also on account of their specific cytological and physiological properties (Barlow et al, 1991;BaluSka et al, l992,1994BaluSka et al, l992, ,1996aBaluSka et al, l992, , 1996cIshikawa and Evans, 1992, 1993, 1995.…”

NO signaling is a key component of the root growth response to nitrate inZea maysL.

“…51 A number of experimental data globally indicates that the transition zone of the root may be considered as a sort of sensory center, enabling the root apex to continuously monitor environment parameters and to trigger appropriate responses. [51][52][53][54][55][56][57][58][59][60][61][62][63] Future studies will be needed to deepen the role of this unique root zone in translating the external stimuli in motoric responses.…”