Tasca Ariel, Alcock Thomas D, Bienert Gerd Patrick
Crop Physiology, TUM School of Life Sciences, Technical University of Munich, Alte Akademie 12, 85354 Freising, Germany.
HEF World Agricultural Systems Center, Technical University of Munich, 85354 Freising, Germany.
Ann Bot. 2025 Jul 9. doi: 10.1093/aob/mcaf142.
A vigorous root system is crucial for maize seedling establishment. Its formation and subsequent plant performance are hindered by nutrient- and water deficiency. Upon germination, maize seedlings develop primary, then seminal roots, covered with pubescent root hairs. Functions of root hairs at this developmental stage remain scarcely understood. This study examined their role during phosphorus- (P) and water limitations during early seedling development at the physiological, elemental, and molecular level, comparing a roothairless maize mutant (rth3) and its isogenic wildtype (WT).
Shoot- and root-system-architecture phenotyping and elemental analysis were performed on 5-day-old rth3 and WT plants experiencing various P- and water-deficient conditions in different growth substrates. Microscopy of root hairs and specific RT-qPCR of various P-nutrition regulators and aquaporins in roots were performed.
WT seedlings responded with a morphologically typical root hair elongation solely to water-reduced but not P-deficient conditions. In contrast, at the molecular level, WT and rth3 responsively upregulated P transporters in roots upon P deficiency, while water channel transcript abundances did not change upon water limitations. Surprisingly, under these adverse seedbed conditions no differences in shoot biomass, shoot nutrient concentrations, shoot water content were detected between the WT and the roothairless mutant which additionally formed a generally shorter total root length compared to the WT. P deficiency caused the development of thicker primary roots in rth3 and significant increase in expression of P transporters compared to the WT.
Germinating rth3 seedlings showed neither disadvantages in terms of shoot vigor, nor with respect to shoot water- and nutrient levels in suboptimal seedbed conditions compared to the WT, despite possessing shorter roots and no root hairs. An increase of the root diameter and P-transporter expression particularly in rth3 seminal roots may have been sufficient to physiologically compensate for the missing root hairs.
强大的根系对玉米幼苗的建立至关重要。养分和水分不足会阻碍其根系的形成及后续植株的生长表现。玉米种子萌发后，先长出初生根，随后是胚根，胚根上覆盖着具柔毛的根毛。目前对于该发育阶段根毛的功能仍知之甚少。本研究在生理、元素和分子水平上，比较了无毛根玉米突变体（rth3）及其同基因野生型（WT），探究了根毛在玉米幼苗早期发育过程中应对磷（P）和水分限制时所起的作用。
对生长在不同生长基质中、处于各种缺磷和缺水条件下的5日龄rth3和WT植株进行地上部和根系结构表型分析以及元素分析。对根毛进行显微镜观察，并对根中各种磷营养调节因子和水通道蛋白进行特异性逆转录定量聚合酶链反应（RT-qPCR）。
野生型幼苗仅在水分减少而非缺磷条件下，会以形态上典型的根毛伸长作为响应。相反，在分子水平上，野生型和rth3在缺磷时根系中磷转运体均有响应性上调，而在水分受限情况下水通道转录本丰度没有变化。令人惊讶的是，在这些不利的苗床条件下，野生型和无毛根突变体之间在地上部生物量、地上部养分浓度、地上部含水量方面均未检测到差异，而且与野生型相比，无毛根突变体的总根长通常更短。缺磷导致rth3的初生根变粗，与野生型相比，磷转运体的表达显著增加。
与野生型相比，萌发的rth3幼苗尽管根系较短且无根毛，但在次优苗床条件下，其地上部活力、地上部水分和养分水平均无劣势。根直径的增加以及尤其是rth3胚根中磷转运体表达的增加，可能已足以在生理上弥补根毛的缺失。
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