植物学

植物学

来源出版物：Journal of Integrative Plant Biology， 2014， 57（1）：93-105联系邮箱：Yuuki Sakai， yuukis0110@gmail.com

封面介绍：Actin-dependent chloroplast anchoring is crucial to maintain specific distribution patterns of chloroplasts.Using a centrifugation assay， Sakai et al.（pp.93-105） demonstrate for the aquatic angiosperm， Vallisneria sp.， that an initial step of chloroplast movement in response to high-intensity blue light is loss of anchorage from the plasma membrane.In addition， they clone photoropin 1 & 2， the putatively responsible blue-light photoreceptors， increasing the utility of this experimentally tractable plant for studies of chloroplast motility.

Blue-light-induced rapid chloroplast de-anchoring in Vallisneria epidermal cells

Yuuki Sakai， Shin-ichiro Inoue， Akiko Harada， et al.

In the outer periclinal cytoplasm of leaf epidermal cells of an aquatic angiosperm Vallisneria， blue light induces “chloroplast de-anchoring”， a rapid decline in the resistance of chloroplasts against centrifugal force.Chloroplast de-anchoring is known induced within 1 min of irradiation with high-fluence-rate blue light specifically， preceding the commencement of chloroplasts migration toward the anticlinal cytoplasm.However， its regulatory mechanism has remained elusive， although pharmacological analysis suggested that a calcium release from intracellular calcium stores is necessary for the response.In search of the responsible photoreceptors， immunoblotting analysis using antibodies against phototropins demonstrated that cross-reactive polypeptides of 120-kDa exist in the plasma-membrane fraction prepared from the leaves.In vitro phosphorylation analysis revealed that 120-kDa polypeptides were phosphorylated by exposure to blue light in a fluence-dependent manner.The blue-light-induced phosphorylation activity was sensitive to a Ser/Thr kinase inhibitor， staurosporine， and unusually was retained at a high level for a long time in darkness.Furthermore， phototropin gene homologs（Vallisneria PHOTOTROPIN1 and PHOTOTROPIN2） expressed in leaves were isolated.We propose that calcium-regulated chloroplast de-anchoring， possibly mediated by phototropins， is an initial process of the blue-light-induced avoidance response of chloroplasts in Vallisneria.

Avoidance response of chloroplasts；blue-light response；chloroplast de-anchoring；cytoplasmic calcium；phototropin