Exploration of the intricacies of low light-induced changes in cigar tobacco leaf anticlinal growth: A holistic approach from anatomical and hormonal levels to gene expression

Abstract

Cigar tobacco stands as a pivotal economic crop, with its leaf growth and development profoundly influenced by light intensity. It specifically aims to investigate how leaf morphology and anticlinal growth respond to varying light intensities, including normal light intensity (NL-300 mol m-2 s-1) and lower light intensity (LL-100 mol m-2 s-1). The research elucidates significant morphological shifts in cigar tobacco leaves under LL, revealing notable alterations in leaf area, leaf length, and leaf width. Early reductions in leaf dimensions, ranging from 30% to 48%, were succeeded by a substantial enhancement in expansion rates from day 9 to day 26, contributing to expanded leaf surfaces at later stages. Upper epidermis thickness declined by 29-19%, with a notably slower expansion rate in the initial 20 days. Palisade cell length consistently decreased by 52-17%, corresponding with upper epidermis trends. Spongy tissue thickness was reduced by 31-12%, with a slower expansion rate in LL for the initial 14 days, and leaf thickness dropped by 34-11%. LL resulted in slower leaf anticlinal expansion, leading to reduced leaf thickness (LT). LL significantly influenced phytohormones in cigar tobacco leaves. Gibberellic acid (41% to 16%) and auxin (20% to 35%) levels were found in higher amounts, while cytokinin levels (19% to 5%) were lowered compared to NL, indicating the intricate regulatory role of light in hormonal dynamics. The observed increase in LT and different cell layers at specific time points (day 8, day 12, day 24, and day 28) under LL, although lower than NL, may be attributed to elevated expression of genes related to cell expansion, including GRF1, XTH, and SAUR19 at those time points. This comprehensive understanding elucidates the intricate mechanisms by which light intensity orchestrates the multifaceted processes governing leaf anatomy and anticlinal expansion in cigar tobacco plants.