Abstract
Summary Far‐red (FR) light promotes fruit growth by increasing dry mass partitioning to fruits, but the mechanism behind this is unknown. We hypothesise that it is due to an increased fruit sink strength as FR radiation enhances sugar transportation and metabolism.Tomato plants were grown with or without 50–80 μmol m−2 s−1 of FR radiation added to a common background 150–170 μmol m−2 s−1 red + blue light‐emitting diode lighting. Potential fruit growth, achieved by pruning each truss to one remaining fruit, was measured to quantify fruit sink strength. Model simulation was conducted to test whether the measured fruit sink strength quantitatively explained the FR effect on dry mass partitioning. Starch, sucrose, fructose and glucose content were measured. Expression levels of key genes involved in sugar transportation and metabolism were determined.FR radiation increased fruit sink strength by 38%, which, in model simulation, led to an increased dry mass partitioned to fruits that quantitatively agreed very well with measured partitioning. FR radiation increased fruit sugar concentration and upregulated the expression of genes associated with both sugar transportation and metabolism.This is the first study to demonstrate that FR radiation stimulates dry mass partitioning to fruits mainly by increasing fruit sink strength via simultaneous upregulation of sugar transportation and metabolism.
Highlights
The recent development of light-emitting diodes (LED) has stimulated research on light quality to achieve higher crop productivity with more health benefits but less energy consumption (Pattison et al, 2018)
In tomato, which is a crop of both economical and scientific importance, FR radiation significantly increased the fraction of dry mass partitioned to fruits and this increase was shown to be the main explanation of yield increase under additional FR radiation (Ji et al, 2019)
The plants without fruit pruning were used to test the overall effect of FR radiation on partitioning to fruits, while those pruned to five fruits per truss were used to test whether partitioning was affected by FR radiation, independent of the potential effects of FR radiation on fruit number
Summary
The recent development of light-emitting diodes (LED) has stimulated research on light quality to achieve higher crop productivity with more health benefits but less energy consumption (Pattison et al, 2018). In tomato, which is a crop of both economical and scientific importance, FR radiation significantly increased the fraction of dry mass partitioned to fruits and this increase was shown to be the main explanation of yield increase under additional FR radiation (Ji et al, 2019). An enhanced hydrolysis of sucrose in sink organs may increase yield (Baroja-Fernandez et al, 2009) by increasing the gradient of sucrose concentration from source to sink (Ho, 1996; Koch, 2004; Fridman et al, 2004) and enhancing cell growth and sugar accumulation (Jin et al, 2009). APGase, for example, is a key regulatory enzyme of starch biosynthesis and its activity positively correlates with fruit sugar content in tomato (Petreikov et al, 2006)
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