This study aims to explore the impact of different fruit shapes on vascular bundle distribution and their relationship with water transport in grape fruits. It focused on the growth patterns, vascular bundle structure, and water transport functions in five grape varieties with distinct fruit shapes, providing a theoretical basis for managing different fruit-shaped grapes in production.

Under uniform cultivation and management, four-year-old plants of ‘Xiao Lajiao’ (curved fruit), ‘Sweet Sapphire’ (long-cylindrical fruit), ‘Muscat Hamburg’ (round fruit), ‘Shine Muscat’ (elliptical fruit), and hormone-treated ‘Shine Muscat’ (inverted-ovate fruit, treated with GA3+CPPU) were used as experimental materials. The morphology and spatial distribution of vascular bundles in fruits of contrasting shapes were examined using hand sectioning, paraffin sectioning, and dye-tracer techniques. Xylem vessel number and diameter were quantified using Image J, and hydraulic conductivity was calculated with Hagen-Poiseuille equation to assess the water-transport efficiency of fruit vascular bundle in different fruit shapes.

Pronounced differences were observed in vascular bundle architecture among grape fruits of contrasting shapes. After entering the fruit, the pedicel bundles diverged into peripheral, central, and embryo (in seeded cultivars) systems. ‘Xiao Lajiao’ had the most primary peripheral vascular bundles, forming numerous branches towards the fruit apex, resulting in the highest vascular bundle density in the upper fruit. ‘Sweet Sapphire’ had abundant and highly dense peripheral vascular bundles in the fruit’s middle and lower parts. Hormone-treated ‘Shine Muscat’ showed significantly increased vascular bundle number and density, indicating that exogenous hormones promote peripheral vascular bundle distribution. In terms of vascular bundle structure and water transport, ‘Sweet Sapphire’ had the largest peripheral vascular bundle cross-sectional area, while ‘Xiao Lajiao’ had the largest central vascular bundle cross-sectional area. Long-shaped grape fruits exhibited larger vascular bundle vessel diameters, resulting in higher hydraulic conductivity. Hormone treatment increased the peripheral vascular bundle area and vessel diameter in ‘Shine Muscat’, enhancing water transport. The water transport rate peaked at the green-hard stage. ‘Xiao Lajiao’ had the highest rate at 16.67 cm·h^-1, while ‘Muscat Hamburg’ had the lowest at 5.67 cm·h^-1. During the veraison, when the water transport rate decreased, the maximum water transport rate of ‘Sweet Sapphire’ grapes was 4.34 cm·h^-1. At the mature stage, the rate declined further, but ‘Xiao Lajiao’ still maintained the highest rate at 0.69 cm·h^-1 due to its vascular bundle advantages. Hormone-treated ‘Shine Muscat’ showed improved water transport rates across all stages, highlighting the close relationship between water transport rate and vascular bundle area and vessel diameter.

The structure and distribution of vascular bundles in grape fruits with different shapes are different, which affects the water transport function of grape fruits.

The accumulation of starch in chloroplast of grape leaves increased with leaf maturation, but the related molecular mechanism has not been reported. In this study, the potential related genes were screened in order to clarify the molecular regulation mechanism of starch accumulation in chloroplast of grape leaves with different leaf ages.

Two years old ‘Pinot Noir’ grapes (Vitis vinifera L.) were used as plant materials to investigate the dynamic changes of starch accumulation in chloroplast of leaves with different ages. The RNA sequencing technology was used to characterize the differently expressed genes (DEGs) involved in starch and sucrose metabolism in leaves with different ages. The expression levels of several key candidate genes were detected by using real-time quantitative qPCR.

The starch grains in NL (undeveloped leaves) were smallest in volume and lowest in number compared with these in GL (growing leaves) and ML (mature leaves). With the increase of leaf ages, the volume and amount of starch grains in GL and ML also increased. A total of 58.57 GB valid data was obtained by RNA-sequencing. Differentially expressed genes mainly involved in starch and sucrose metabolism pathway for the leaves with different ages. The genes involved in the process of sucrose conversion into starch synthesis precursor adenosine diphosphate glucose (ADP) showed up-regulated expression level with the increase of leaf ages, including cell wall invertase (CWINV), phosphoglucomutase (PGM), and ADP-glucose pyrophosphorylase (AGPase). The genes involved in starch synthesis and hydrolysis also presented up-regulated expression level with the increase of leaf ages, including soluble starch synthase (SSⅠ), starch branching enzyme (SBE), α-amylase (AMY), and β-amylase (BAM). AGPase, SSⅠ and SBE played an important role in synthesis of amylopectin with semi-crystalline structure.

With the increase of leaf ages, the starch accumulation in chloroplast also increased. AGPase, SSⅠ and SBE genes could be the key genes involved in the regulation of starch accumulation in chloroplast of grape leaves.