Carbohydrate control over carotenoid build‐up is conditional on fruit ontogeny in clementine fruits

Abstract

The final contents of primary and secondary metabolites of the ripe fruit depend on metabolic processes that are tightly regulated during fruit ontogeny. Carbohydrate supply during fruit development is known to influence these processes but, with respect to secondary metabolites, we do not really know whether this influence is direct or indirect. Here, we hypothesized that the sensitivity of clementine fruit metabolism to carbohydrate supply was conditional on fruit developmental stage. We applied treatments increasing fruit load reversibly or irreversibly at three key stages of clementine (Citrus clementina Hort. ex Tan.) fruit development: early after cell division, at the onset of fruit coloration (color break) and near maturity. The highest fruit load obtained by early defoliation (irreversible) had the highest impact on fruit growth, maturity and metabolism, followed by the highest fruit load obtained by early shading (reversible). Final fruit size decreased by 21 and 18% in these early irreversible and reversible treatments, respectively. Soluble sugars decreased by 18% in the early irreversible treatment, whereas organic acids increased by 46 and 29% in these early irreversible and reversible treatments, respectively. Interestingly, total carotenoids increased by 50 and 18%, respectively. Changes in leaf starch content and photosynthesis supported that these early treatments triggered a carbon starvation in the young fruits, with irreversible effects. Furthermore, our observations on the early treatments challenge the common view that carbohydrate supply influences positively carotenoid accumulation in fruits. We propose that early carbon starvation irreversibly promotes carotenoid accumulation.

Buffering growth variations against water deficits through timely carbon usage

“…To probe the effect of carbon availability on fruit growth in field conditions, a defoliation treatment was applied on girdled fruiting branches from adult clementine trees to obtain three levels of leaf-to-fruit ratio: 5, 15, and 30 leaves per fruit. The leaf-to-fruit ratio 30 corresponds to conditions of non-limiting carbon availability, and was considered as the control (Poiroux-Gonord et al, 2013). For masses and carbohydrate measurements, five fruits per level of leaf-to-fruit ratio were collected regularly in the morning (10:00, local time) from September to March during the 2008–2009 season.…”

“…Only fully expanded flowers from May 5th to May 15th 2008 were selected to obtain fruits of similar age. After the completion of cell division in the fruit (at the end of July under Mediterranean climate; Tadeo et al, 2008), the leaf-to-fruit ratio was set to 30, 15, or 5 leaves per fruit to obtain a control, moderate or low carbon availability (Poiroux-Gonord et al, 2013). The 120 selected fruiting branches were composed of 1-year shoots from the spring flush of the previous season.…”

“…Then, the pulp material was ground to a fine powder and stored at -80°C for subsequent analyzes. Sugar analyzes of the pulp were performed by HPLC according to the method previously described in Poiroux-Gonord et al (2013).…”

Antioxidant and enzymatic responses to oxidative stress induced by pre-harvest water supply reduction and ripening on mango (Mangifera indica L. cv. ‘Cogshall’) in relation to carotenoid content

“…The effects of reduced water supply on carotenoid accumulation have not been widely studied, with the exception of tomato fruit in which a consistent increase lycopene content but no effect on ␤-carotene or xanthophyll contents was reported (Stefanelli et al, 2010). It is important to highlight the fact that the biosynthesis of carotenoid remains exponential during ripening and that we had no evidence in this study to suggest an upregulation in synthesis linked to fruit growth conditions, such as carbon limitation (Poiroux-Gonord et al, 2013). However, such conditions unbalanced the relative carotene content.…”

Prospects for Using Environmental Levers in Greenhouses to Stimulate Plant Defences and the Quality of Fruits and Vegetables

“…This idea certainly has merits as far as defence compounds are concerned, but there are contradictory observations. In leaves, accumulation of carbohydrates generally represses the synthesis of carotenoids; whereas in fruits, low availability of carbohydrates may reduce carotenoid concentrations of (Poiroux-Gonord et al, 2013a). It is interesting to note that there are links between the stress and carbon theories.…”