Comparative Transcriptome and Anatomic Characteristics of Stems in Two Alfalfa Genotypes

Abstract

Stems are more important to forage quality than leaves in alfalfa. To understand lignin formation at different stages in alfalfa, lignin distribution, anatomical characteristics and transcriptome profile were employed using two alfalfa cultivars. The results showed that the in vitro true digestibility (IVTD) of stems in WL168 was significantly higher than that of Zhungeer, along with the significantly lower neutral detergent fiber (NDF), acid detergent fiber (ADF) and lignin contents. In addition, Zhungeer exhibited increased staining of the xylem areas in the stems of different developmental stages compared to WL168. Interestingly, the stems of WL168 appeared intracellular space from the stage 3, while Zhungeer did not. The comparative transcriptome analysis showed that a total of 1993 genes were differentially expressed in the stem between the cultivars, with a higher number of expressed genes in the stage 4. Of the differentially expressed genes, starch and sucrose metabolism as well as phenylpropanoid biosynthesis pathways were the most significantly enriched pathways. Furthermore, expression of genes involved in lignin biosynthesis such as PAL, 4CL, HCT, CAD, COMT and POD coincides with the anatomic characteristics and lignin accumulation. These results may help elucidate the regulatory mechanisms of lignin biosynthesis and improve forage quality in alfalfa.

Effects of leaf and stem maturation on nutritional value in Megathyrsus maximus

“…Moreover, several reports showed that forage growth is accompanied by increased lignin content with secondary cell wall thickening, which limits forage cell wall digestion by ruminants. 44,45 However, NDF and ADL as values of leaf blades were much lower than those of stems in all the M. maximus genotypes. This may be because the leaf blade consists mainly of parenchyma cells, while the stems have more sclerenchyma cells.…”

“…who observed a continuous increase in the accumulation of lignin and significant change in its composition in internodes at reproductive stages. Moreover, several reports showed that forage growth is accompanied by increased lignin content with secondary cell wall thickening, which limits forage cell wall digestion by ruminants 44,45 …”

“…The digestion potential of forage tissues decreases in the following order in the ruminant: parenchyma > phloem > epidermis > bundle sheath > xylem and sclerenchyma. 45 As some forage tissues are rapidly digestible while others impair digestibility and intake, analyses of the proportions of these tissues should indicate potential forage digestibility. Identifying the tropical grass varieties with the highest nutritional value is important for the purposes of plant breeding.…”

“…Quantitative plant anatomy has become a significant tool for the evaluation of forage quality, used in many studies as a complement to evaluate the digestibility of leaf blades tissues. The digestion potential of forage tissues decreases in the following order in the ruminant: parenchyma > phloem > epidermis > bundle sheath > xylem and sclerenchyma 45 . As some forage tissues are rapidly digestible while others impair digestibility and intake, analyses of the proportions of these tissues should indicate potential forage digestibility.…”

Research Progress on Dormancy Mechanism and Germination Technology of Kobresia Seeds

“…In recent years, much research has been carried out on seed dormancy and germination at home and abroad, certain results have been achieved by this [ 26 , 37 , 38 , 39 , 40 , 41 ], but there are still many problems to be solved. Domestic research on seed dormancy is still unsystematic; the research on the seed dormancy of Kobresia mainly focuses on the following: (1) Dormancy breaking is only treated by physical or chemical methods alone; (2) variable temperature is merely combined with other physical or chemical methods; (3) chemical methods for dormancy breaking are very limited, mainly using NaOH, GA 3 , and other reagents; and (4) at present, research on the dormancy and germination mechanism of Kobresia mainly focuses on physiological experiments.…”