Abstract
BackgroundBoth underground rhizomes/buds and above-ground Moso bamboo (Phyllostachys heterocycla) shoots/culms/branches are connected together into a close inter-connecting system in which nutrients are transported and shared among each organ. However, the starch storage and utilization mechanisms during bamboo shoot growth remain unclear. This study aimed to reveal in which organs starch was stored, how carbohydrates were transformed among each organ, and how the expression of key genes was regulated during bamboo shoot growth and developmental stages which should lay a foundation for developing new theoretical techniques for bamboo cultivation.ResultsBased on changes of the NSC content, starch metabolism-related enzyme activity and gene expression from S0 to S3, we observed that starch grains were mainly elliptical in shape and proliferated through budding and constriction. Content of both soluble sugar and starch in bamboo shoot peaked at S0, in which the former decreased gradually, and the latter initially decreased and then increased as shoots grew. Starch synthesis-related enzymes (AGPase, GBSS and SBE) and starch hydrolase (α-amylase and β-amylase) activities exhibited the same dynamic change patterns as those of the starch content. From S0 to S3, the activity of starch synthesis-related enzyme and starch amylase in bamboo rhizome was significantly higher than that in bamboo shoot, while the NSC content in rhizomes was obviously lower than that in bamboo shoots. It was revealed by the comparative transcriptome analysis that the expression of starch synthesis-related enzyme-encoding genes were increased at S0, but reduced thereafter, with almost the same dynamic change tendency as the starch content and metabolism-related enzymes, especially during S0 and S1. It was revealed by the gene interaction analysis that AGPase and SBE were core genes for the starch and sucrose metabolism pathway.ConclusionsBamboo shoots were the main organ in which starch was stored, while bamboo rhizome should be mainly functioned as a carbohydrate transportation channel and the second carbohydrate sink. Starch metabolism-related genes were expressed at the transcriptional level during underground growth, but at the post-transcriptional level during above-ground growth. It may be possible to enhance edible bamboo shoot quality for an alternative starch source through genetic engineering.
Highlights
Both underground rhizomes/buds and above-ground Moso bamboo (Phyllostachys heterocycla) shoots/culms/branches are connected together into a close inter-connecting system in which nutrients are transported and shared among each organ
Starch synthesis occurs in the following steps: starch synthesis substrates are catalysed by Adenosine diphosphate glucose pyrophosphorylase (AGPase), amylose is synthesized by Granule-bound starch synthase (GBSS), and amylopectin is synthesized by Soluble starch synthase (SSs) and Starch branching enzyme (SBE) (Starch Branching Enzyme/Q enzyme) [4,5,6]
Based on bamboo shoot growth and development characteristics, bamboo shoots and rhizomes in the four different growth and developmental stages were chosen for this study: dormancy in winter (S0, underground dormant buds), upearthing growth from underground in early spring (S1, winter shoots are broken in dormancy and are ready for emerging as spring shoots), rapid growth (S2, spring shoots are approximately 50 cm high aboveground) and slow growth (S3, spring shoots are approximately 150 cm high aboveground) (Fig. 1a)
Summary
Both underground rhizomes/buds and above-ground Moso bamboo (Phyllostachys heterocycla) shoots/culms/branches are connected together into a close inter-connecting system in which nutrients are transported and shared among each organ. At different developmental stages of wheat grains, the starch accumulation rate is significantly positively correlated with GBSS and SBE activities, and the accumulation process of amylopectin, amylose and the starch content after pollination follows a logistic growth equation [10]. The expression of starch metabolism-encoding genes shows tissue and developmental period specificity. These genes are involved in the four main processes: construction of cellular machinery, embryonic development, starch synthesis in the embryo and kernel development [11]. The genes and starch properties of Moso bamboo are very similar to those of rice [19], but there are few studies on starch metabolism during the growth process of bamboo shoots
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