Green seed photosynthesis: What is it? What do we know about it? Where to go?

Chlorophyllous (chlorophyll-containing green) seeds can carry out photosynthesis, which partially meets the energy demand of the growing embryo embedded in them. However, as compared to the leaves, green seeds synthesize major biopolymers such as fatty acids, which are exploited as energy repositories rather than translocating to other sinks. Green seed photosynthesis is characterized with a large antenna size of Photosystem II (PSII), which enables the seeds to deal with low light saturation point and operate under a lower level of plastoquinone pool than in the leaves. In addition to the above features, the low chlorophyll (Chl) a/b ratio (1.51) also accounts for the reduced photosynthetic yield in green seeds as in the case of shade plants. The presence of chlorophylls, involved in the photosynthesis of seeds, ensures the maintenance of oxygen levels within the seeds and hence supports adequate cellular respiration in addition to providing the nutrients for the growing embryo. In this review, we provide an overview of the green seed photosynthesis, emphasizing the physiological role of the 'residual' chlorophyll in the seeds by highlighting the studies that have contributed towards the advancement of the green seed physiology.