Relationships Of Leaf Vein Density With Photosynthetic Characteristic And Water Balance In Sorghum And Perilla

Perilla (Perilla frutescens L.) originated in East Asia, was widely cultivated in China. As a type of nutritious vegetable and traditional medicinal plant, perilla has been attracted more attentions. With the global drought is more and more serious, it is crucial to improve drought tolerance and water use efficiency. Leaf vein is an important structure for plant photosynthesis and water transportation. It is very important to study the relation between leaf vein density and photosynthetic characteristics, and the influences of leaf structure on the photosynthetic characteristics and water use efficiency.The main findings are as follows.(1) Compared with perilla leaves, sorghum leaves had higher leaf vein density, stomatal conductance (Gs) and leaf hydraulic conductance (Kleaf), whereas, perilla leaves had a higher stomatal density than that in sorghum leaves. For sorghum leaves, the proportion of stomatal density on the adaxial side accounted for 38.42% of the total stomatal density, which is significantly higher than the perilla leaves. Sorghum leaves developed with higher vein density have higher net photosynthetic rate, while perilla leaves evolved with lower vein density have lower net photosynthetic rate.(2) Water stress significantly decreased leaf area, vein diameter, stomatal size, and increased vein density and stomatal density. The thickness of mesophyll tissue, the area of mesophyll cell surfacing intercellular air spaces and the area of chloroplast surfaces facing the intercellular spaces were decreased. In addition, the net photosynthetic rate (Pn), stomatal conductance (Gs) and leaf hydraulic conductance (Kieaf) decreased greatly, while water use efficiency increased markedly. Due to the reduction of vein diameter is proportional to the reduction of leaf hydraulic conductance (Kleaf), we deduced that vein diameter may be the key factor influencing the leaf hydraulic conductance (Kieaf).In summary, we found that sorghum leaves with higher photosynthetic rate was related to the higher vein density. But there is not a rigidly collaborative variation between leaf vein density and stomatal density. The findings of the present study are important for adaptability of plant photosynthesis. Under water stress, sorghum and perilla leaves had increased leaf density and stomatal density, decreased vein diameter and other structure changes to maintain the photosynthetic rate and the balance between water supply and demand, so as to improve the water use efficiency. Compared with perilla, sorghum had higher vein density and lower stomatal density, which were beneficial to maintaining water supply and demand balance during water stress.