Monocot-like leaf structure and trichome-water relations in early growth stages of the C3 plant sand rice (Agriophyllum squarrosum)

Abstract

Sand rice (Agriophyllum squarrosum (L.) Moq.), a species of Amaranthaceae sensu lato, is an annual psammophyte found mainly on sand dunes in arid and semi-arid regions of Central Asia. Trichomes on the leaf surface are a key adaptive feature of sand rice, however, their ecophysiological functions remain to be elucidated. In this study, the anatomical analysis of a leaf reveals that the foliage is characterized by its isobilateral and amphistomatic nature. Together with an average δ¹³C value of −28.57 ‰, these findings indicate that sand rice is a C₃ plant. Utilizing a trichome-defective mutant (Agriophyllum squarrosum trichomeless1, astcl1) identified from an EMS mutagenesis library by our group, alongside the wild type Shapotou (SPT), we observed that both epidermal surfaces on SPT leaves exhibit dense and dendritic trichomes, forming rough leaf boundary layers. Chlorophyll leaching analysis revealed that SPT has a higher epidermal permeability, with 86.32 % of chlorophylls leaching out within 30 minutes, compared to only 24.18 % for astcl1. The astcl1 leaf displayed a higher leaf wettability, lower water loss, and thicker cuticle compared to SPT leaves, which may be associated with trichomes serving as the primary pathway for nonstomatal water movement. This is supported by the observation that toluidine blue staining is more intense in trichomes than in pavement cells. Our findings reveal that the correlation between trichomes and the cuticle appears to be a critical factor in managing water loss and overall plant hydration, highlighting the significant role of trichomes in the adaptation of sand rice to desert environments.