In grapevines, as in other plants, sucrose and its constituents glucose and fructose are fundamentally important and carry out a multitude of roles. The aims of this review are three-fold. First, to provide a summary of the metabolism and transport of sucrose in grapevines, together with new insights and interpretations. Second, to stress the importance of considering the compartmentation of metabolism. Third, to outline the key role of acid invertase in osmoregulation associated with sucrose metabolism and transport in plants.

The cultivation of spinach (Spinacia oleracea L.) has been increasing during the last years in controlled environment agriculture, where light represents a key factor for controlling plant growth and development and the highest energetic costs. The aim of the experiment was to evaluate the plant’s response to two light intensities, corresponding to an optimal and a reduced level, in terms of the photosynthetic process, photoassimilates partitioning, and the biosynthesis of sucrose and starch. Plants of spinach cv. ‘Gigante d’Inverno’ were grown in a phytotron under controlled conditions, comparing two values of photosynthetic photon flux density (PPFD), 800 μmol m⁻² s⁻¹ (800 PPFD) and 200 μmol m⁻² s⁻¹ (200 PPFD), at a 10 h light/14 h dark regime. Compared to 800 PPFD, under 200 PPFD, plants showed a reduction in biomass accumulation and a redirection of photoassimilates to leaves, determining a leaf expansion to optimize the light interception, without changes in the photosynthetic process. A shift in carbon partitioning favouring the synthesis of starch, causing an increase in the starch/sucrose ratio at the end of light period, occurred in low-light leaves. The activity of enzymes cFBAse, SPS, and AGPase, involved in the synthesis of sucrose and starch in leaves, decreased under lower light intensity, explaining the rate of accumulation of photoassimilates.

The characteristics of plum fruits of three different species were investigated throughout their development (including over-ripening). The content of primary and secondary metabolites was expressed as amount per gram DW (dry weight) and per fruit in order to obtain information about the balance between their synthesis and dissimilation at different stages of fruit development. In all the plums, during the first stages of development, glucose was the most abundant sugar, whereas sucrose increased during ripening. There was no decrease in malate content per fruit before the commercial harvesting time of any of the plums, whereas a decrease was observed during over-ripening. In general, both the total phenol content and the contents of individual phenols in the flesh expressed on gram DW decreased throughout development, whereas their content per fruit increased, indicating that these decreases were due to a dilution effect arising from the expansion of the flesh. During the development of the flesh, the increase in the contents of the investigated metabolites per fruit shows that there was no net dissimilation of malate up to commercial harvest and of phenols throughout fruit development. Good correlations between the content of phenols to antioxidant activity were found. Shiro flesh, during the last part of fruit development, had lower total carbohydrate and polyphenol contents, lower antioxidant activities, and a higher malate content than the flesh of the other two genotypes.

Photosynthesis and carbohydrate accumulation in maize genotypes ( Zea mays L.) VA-36 and A-619, ranked as possessing low and high sensitivity to low temperature, were studied in relation to regrowth after transfer from day/night temperatures of 16/12˚C to 25/20˚C. Plants were grown for 45 days at 25/20 or 16/12˚C, or transferred after 45 days from 16/12˚C to 25/20˚C for 27 days. Photosynthesis of both genotypes after a 45-day growth at 16/12˚C was lower than at 25/20˚C. When the photosynthesis of plants at 16/12˚C was measured at 25˚C it was as high as the photosynthesis of plants at 25˚C in VA-36, while it remained lower in A-619. A strong reduction of rubisco content was observed in the sensitive genotype and is suggested as the cause of photosynthesis limitation that was still observed after recovery at 25/20˚C. After a 45-day growth at 16/12˚C, a reduction of sucrose and, to a lesser extent, starch content was observed. Biomass accumulation was also reduced in both genotypes. Transfer from 16/12 to 25/20˚C increased photosynthesis, partially restored sucrose but not starch content and induced a rapid regrowth in VA-36. Conversely, photosynthesis, carbohydrate content and regrowth remained low in A-619. It is suggested that for the two genotypes, regrowth is dependent on the integrity of the photosynthetic apparatus which contributes to sensitivity to low temperatures.