PJB-2017-679
Weak stem under shade reveals the lignin reduction behavior
Sajad Hussain
Abstract
Shade caused by neighboring plants or tall stature crop in intercropping, and solar diming has become a chronic constraint in harvesting good yield of short stature crop. It is globally accepted that shade influences many aspects of plant growth and development, including weak stems and susceptibility to lodging. Shade reflects the effect of environment on plant anatomical, morphological and physiological characteristics, thus reducing the physical strength of stem in crops by increasing the length of cell wall and loosening of cell wall protein. In addition, higher plant height, increased internodal length, reduced xylem, low photosynthesis are the palpable anatomical and morphophysiological changes under shade stress, respectively. In shaded plants lignin deposition in vascular bundle and sclerenchyma cells of stem is decreased. Lignin is a light sensitive phenolic compound as shading decreases the transcript abundance of a phenolic compounds (flavone and lignin) related gene. Shading significantly influences the metabolic activities, Phenylalanine ammonia-lyase (PAL), Peroxidase (POD), 4-coumarate: CoA ligase (4CL) and cinnamyl alcohol dehydrogenase (CAD) involved in lignin biosynthesis. Furthermore, suppression of lignin biosynthesis activities by abiotic stresses causes abnormal phenotypes such as collapsed xylem, bending stems, and growth retardation. In this review the underlying mechanisms will illustrate that under shading conditions reduced lignin content results the slender, weak and unstable stem. The objective of this review was to elaborate lignin biosynthesis and its variability under stressful environmental conditions, especially in shade stress environment. The effects of shade on stem lignin metabolism are discussed on morphogenic, physiological and proteomic levels.
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