Different effects of phospholipase Dζ2 and non‐specific phospholipase C4 on lipid remodeling and root hair growth in Arabidopsis response to phosphate deficiency

Phosphate (Pi) deficiency in soils is a major limiting factor for plant growth. In response to Pi deprivation, one prominent metabolic adaptation in plants is the decrease in membrane phospholipids that consume approximately one‐third cellular Pi. The level of two phospholipid‐hydrolyzing enzymes, phospholipase Dζ2 (PLDζ2) and non‐specific phospholipase C4 (NPC4), is highly induced in Pi‐deprived Arabidopsis. To determine the role of PLDζ2 and NPC4 in plant growth under Pi limitation, Arabidopsis plants deficient in both PLDζ2 and NPC4 (npc4pldζ2) were generated and characterized. Lipid remodeling in leaves and roots was analyzed at three different durations of Pi deficiency. NPC4 affected lipid changes mainly in roots at an early stage of Pi deprivation, whereas PLDζ2 exhibited a more overt effect on lipid remodeling in leaves at a later stage of Pi deprivation. Pi deficiency‐induced galactolipid increase and phospholipid decrease were impeded in pldζ2 and npc4pldζ2 plants. In addition, seedlings of npc4pldζ2 had the same root hair density as pldζ2 but shorter root hair length than pldζ2 in response to Pi deficiency. The loss of NPC4 decreased root hair length but had no effect on root hair density. These data suggest that PLDζ2 and NPC4 mediate the Pi deprivation‐induced lipid remodeling in a tissue‐ and time‐specific manner. PLDζ2 and NPC4 have distinctively different roles in root hair growth and development in response to Pi deprivation; PLDζ2 negatively modulates root hair density and length, whereas NPC4 promotes root hair elongation.     

Arabidopsis ROOT HAIR DEFECTIVE3 is involved in nitrogen starvation-induced anthocyanin accumulation

Anthocyanin accumulation is a common phenom-enon seen in plants under environmental stress. In this study, we identified a new allele of ROOT HAIR DEFECTIVE3 (RHD3) showing an anthocyanin overaccumulat...     

低磷供应对拟南芥根系构型的影响

在人工气候箱中,采用Johnson培养基对拟南芥在低磷供应条件下根系构型的变化进行了研究,结果表明：拟南芥在磷饥饿诱导下,主根缩短,侧根密度、根毛的数量和长度显著增加,并且,根尖到第一侧根和第一根毛的距离也大大缩短。这些改变增加了根系比表面积,并且使得根系分布更加靠近土壤表层,有利于提高植物吸收土壤中有机磷的效率。低磷胁迫还导致拟南芥根系分生组织区细胞形状变异,柱细胞数量减少;主根生长和细胞伸长的动力学分析显示,磷饥饿促使拟南芥主根生长变缓,细胞长度随磷饥饿程度的加深迅速缩小。CycB1;1:GUS染色分析结果表明,低磷破坏拟南芥根系分生组织细胞分裂能力,这些结果说明磷胁迫同时抑制了细胞的伸长和分裂,从而引起拟南芥主根的缩短。     

Constitutive Autophagy in Plant Root Cells

In previous studies, using a membrane-permeable protease inhibitor, E-64d, we showed that autophagy occurs constitutively in the root cells of barley and Arabidopsis. In the present study, a fusion protein composed of the autophagy-related protein AtAtg8 and green fluorescent protein (GFP) was expressed in Arabidopsis to visualize autophagosomes. We first confirmed the presence of autophagosomes with GFP fluorescence in the root cells of seedlings grown on a nutrient-sufficient medium. The number of autophagosomes changed as the root cells grew and differentiated. In cells near the apical meristem, autophagosomes were scarcely found. However, a small but significant number of autophagosomes existed in the elongation zone. More autophagosomes were found in the differentiation zone where cell growth ceases but the cells start to form root hair. In addition, we confirmed that autophagy is activated under starvation conditions in Arabidopsis root cells. When the root tips were cultured in a sucrose-free medium, the number of autophagosomes increased in the elongation and differentiation zones, and a significant number of autophagosomes appeared in cells near the apical meristem. The results suggest that autophagy in plant root cells is involved not only in nutrient recycling under nutrient-limiting conditions but also in cell growth and root hair formation.

Addendum to:

AtATG Genes, Homologs of Yeast Autophagy Genes, are Involved in Constitutive Autophagy in Arabidopsis Root Tip Cells

Y. Inoue, T. Suzuki, M. Hattori, K. Yoshimoto, Y. Ohsumi and Y. Moriyasu

Plant Cell Physiol 2006; 47:1641-52