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Abstract：
Apical hook formation is essential for the emergence and stand establishment of cotton plants. Searching for agronomic measures to regulate apical hook formation and clarifying its mechanism are important for full stand establishment in cotton. In this study, cotton seeds were sown at varying seeding rates or depths in sand to determine if and how apical hook formation was regulated by seeding rates or depths. The results showed that deep seeding or low seeding rates increased mechanical pressure and then increased ethylene content by increasing GhACO1 and GhACS2 expression to improve apical hook formation. Silencing of the GhACO1 and GhACS2 genes or exogenous application of 1-methylcyclopropene (1-MCP) decreased the ethylene content and inhibited apical hook formation in the cotton seedlings. Deep seeding, a low seeding rate, or 1-amino cyclopropane-1-carboxylic acid (ACC) treatment increased the expression of GhHLS1 and GhPIF3 genes, but their expression was decreased in theVIGS-ACO1 and VIGS-ACS2 seedlings. Silencing of the GhHLS1 and GhPIF3 genes inhibited apical hook formation, although the expression of GhACO1 and GhACS2 was unchanged. GhPIF3 may act upstream of GhHLS1, as the expression of GhPIF3 in the VIGS-HLS1 seedlings was unchanged, while the expression of GhHLS1 in the VIGS-PIF3 seedlings decreased. These results suggested that raised mechanical pressure could increase ethylene content by inducing GhACO1 and GhACS2 gene expression, which promoted apical hook formation by increasing the expression of GhHLS1. Therefore, adjusting the mechanical pressure through changing the seeding depth or seeding rate is an important means to regulate apical hook formation and emergence.
摘要：
根尖钩的形成对于棉花植物的出现和林分建立至关重要。寻找调节根尖钩形成的农艺措施并阐明其机理对于棉花的全面建立具有重要意义。在这项研究中,将棉花种子以不同的播种率或深度播种在沙子中，以确定是否以及如何通过播种率或深度调节根尖钩的形成。结果表明，深播种或低播种率增加了机械压力，然后通过增加GhACO1和GhACS2表达来增加乙烯含量，以改善根尖钩形成。GhACO1和GhACS2基因的沉默或1-甲基环丙烯（1-MCP）的外源施用降低了棉花幼苗中的乙烯含量并抑制了根尖钩的形成。深度播种，播种率低，或1-氨基环丙烷-1-羧酸（ACC）处理增加了GhHLS1和GhPIF3基因的表达，但它们在VIGS-ACO1和VIGS-ACS2幼苗中的表达降低。GhHLS1和GhPIF3基因的沉默抑制了顶端钩的形成，虽然GhACO1和GhACS2的表达没有改变。GhPIF3可能在GhHLS1上游起作用，因为GhPIF3在VIGS-HLS1幼苗中的表达没有变化，而GhHLS1在VIGS-PIF3幼苗中的表达降低。这些结果表明，提高机械压力可以通过诱导GhACO1和GhACS2基因表达来增加乙烯含量，通过增加GhHLS1的表达促进根尖钩的形成。因此,通过改变播种深度或播种速率来调节机械压力是调节根尖钩形成和出苗的重要手段。
