Low temperature-induced leaf senescence and the expression of senescence-related genes in the panicles of Litchi chinensis

Abstract

Litchi is one of the most important subtropical evergreen fruit trees in Southern Asia. Litchi floral buds are a mix of axillary or apical panicle primordia, leaf primordia, and rudimentary leaves. Under usual winter and early spring conditions, the axillary panicle primordia prevail, and the rudimentary leaves abscise when low temperatures reach a certain threshold. The floral buds ultimately develop into pure panicles. Understanding the regulatory mechanism of rudimentary leaf senescence is of great importance for litchi flowering. In this study, litchi potted trees at the floral differentiation stage were treated with low and high temperatures in order to induce senescence or development of leaves. The microstructure of the petiole base of the rudimentary leaves was determined. The results show several layers of flattened cells forming in the abscission zone of the rudimentary leaves that were treated with low temperatures as well as an obvious boundary regarded as the abscission layer zone. We also determined the gene expression in the leaves with different developmental fate. The results show that the LcRboh, LcMC-1-like, and LcPirin genes were significantly induced in the rudimentary leaves treated with low temperatures, and the expression increased with the proceeding of senescence. The expression of the genes encoding class Ι β-1,3-glucanase and β-xylosidase also increased with the senescence, suggesting their possible involvement in the low temperature-induced senescence of the rudimentary leaves.

Keywords

• abscission zone
• flowering
• litchi
• rudimentary leaves