STUNTED PLANT 1, A Gene Required for Expansion in Rapidly Elongating but Not in Dividing Cells and Mediating Root Growth Responses to Applied Cytokinin

Abstract

To understand the control of spatial patterns of expansion, we have studied root growth in wild type and in the stunted planf 1 mutant, stpl, of Arabidopsis thaliana. We measured profiles of cell length and calculated the distribution of elongation rate. Slow growth of stpl results both from a failure of dividing cell number to increase and from low elongation rates in the zone of rapid expansion. However, elongation of dividing cells was not greatly affected, and stpl and wild-type callus grew at identical rates.*Thus, rapid cellular expansion differs in mechanism from expansion in dividing cells and is facilitated by the STPl gene. Additionally, there was no difference between stpl and wild-type roots for elongation in response to abscisic acid, auxin, ethylene, or gibberellic acid or for radial expansion in response to ethylene; however, stpl responded to cytokinin much less than wild type. In contrast, both genotypes responded comparably to hormones when explants were cultured; in particular, there was no difference between genotypes in shoot regeneration in response to cytokinin. Thus, effects on root expansion mediated by cytokinin, but not effects mediated by other hormones or effects on other cytokinin-mediated responses, require the STPl locus.How is the expansion of plant organs regulated? In the growing zones of most organs, expansion rate is not a constant quantity; rather, there is a well-defined spatial pattern of expansion rate. Although we have learned a considerable amount about how certain compounds, such as auxin, modify overall expansion rate, we have learned less about the control of spatial patterns of expansion rate. Spatial patterns of expansion rate might reflect underlying profiles of concentration of (or sensitivity to) one or more growth-regulating substances, but, in general, this simple explanation has not been validated. Furthermore, expansion in an organ includes dividing cells. Although "growth by cell expansion" is commonly contrasted with

Variation in Growth Rate between Arabidopsis Ecotypes Is Correlated with Cell Division and A-Type Cyclin-Dependent Kinase Activity

“…Automation may ultimately help to resolve this bottleneck. However, to reduce the amount of work involved with the manual analysis, we decided to omit the time-lapse analysis and base the calculations on cell length profile and overall root elongation rate only, analogous to Baskin et al (1995). Crucial for this approach is the determination of the basal margin of the meristem.…”

Cytokinin-Deficient Transgenic Arabidopsis Plants Show Multiple Developmental Alterations Indicating Opposite Functions of Cytokinins in the Regulation of Shoot and Root Meristem Activity

“…One of the possible components of the downstream signaling pathway that controls meristem activity is STUNTED PLANT1 (STP1) (Baskin et al, 1995). As a result of slower cell production, stp1 mutant roots had a slower elongation rate and, more specifically, a reduced response toward cytokinin.…”

Developmentally equivalent tissue sampling based on growth kinematic profiling of Arabidopsis inflorescence stems

“…Closed-box ⁄ arrow indicates the stem position that matches the maximum growth rate of the regression curve (segment 5), plotted as the rightmost vertical dotted line, while the open-box ⁄ arrow indicates the first position below the top of the stem where the growth rate falls to zero (segment 10). debate of the effect of such confinement on actual growth rate (reviewed in Baskin et al, 1995). In our system, stem growth was essentially constrained to a single linear trajectory through use of fine vertical nylon guide lines that permit uninterrupted branching and floral development while constraining circumnutatory movement, without impeding vertical extension (Fig.…”

“…REGR data have also been generated indirectly for a number of species (not including Arabidopsis) through a modeling approach that uses a logistic function conditioned by estimated parameters in order to substitute for the missing velocity field data (Morris & Silk, 1992). This logistic function was used to model strain rates (cell wall expansion), essentially equivalent to REGR, from cell length data (destructive sampling) and overall root growth rate (Baskin et al, 1995).…”