We investigated the role of the oilbody proteins in developing and germinating Arabidopsis thaliana seeds. Seed oilbodies are simple organelles comprising a matrix of triacylglycerol surrounded by a phospholipid monolayer embedded and covered with unique proteins called oleosins. Indirect observations have suggested that oleosins maintain oilbodies as small single units preventing their coalescence during seed desiccation. To understand the role of oleosins during seed development or germination, we created lines of Arabidopsis in which a major oleosin is ablated or severely attenuated. This was achieved using RNA interference techniques and through the use of a T-DNA insertional event, which appears to interrupt the major (18 kD) seed oleosin gene of Arabidopsis and results in ablation of expression. Oleosin suppression resulted in an aberrant phenotype of embryo cells that contain unusually large oilbodies that are not normally observed in seeds. Changes in the size of oilbodies caused disruption of storage organelles, altering accumulation of lipids and proteins and causing delay in germination. The aberrant phenotypes were reversed by reintroducing a recombinant oleosin. Based on this direct evidence, we have shown that oleosins are important proteins in seed tissue for controlling oilbody structure and lipid accumulation.

The present review discusses not only advances in coconut tissue culture and associated biotechnological interventions but also future research directions toward the resilience of this important palm crop. Coconut (Cocos nucifera L.) is commonly known as the 'tree of life'. Every component of the palm can be used to produce items of value and many can be converted into industrial products. Coconut cultivation faces a number of acute problems that reduce its productivity and competitiveness. These problems include various biotic and abiotic challenges as well as an unstable market for its traditional oil-based products. Around 10 million small-holder farmers cultivate coconut palms worldwide on c. 12 million hectares of land, and many more people own a few coconut palms that contribute to their livelihoods. Inefficiency in the production of seedlings for replanting remains an issue; however, tissue culture and other biotechnological interventions are expected to provide pragmatic solutions. Over the past 60 years, much research has been directed towards developing and improving protocols for (i) embryo culture; (ii) clonal propagation via somatic embryogenesis; (iii) homozygote production via anther culture; (iv) germplasm conservation via cryopreservation; and (v) genetic transformation. Recently other advances have revealed possible new ways to improve these protocols. Although effective embryo culture and cryopreservation are now possible, the limited frequency of conversion of somatic embryos to ex vitro seedlings still prevents the large-scale clonal propagation of coconut. This review illustrates how our knowledge of tissue culture and associated biotechnological interventions in coconut has so far developed. Further improvement of protocols and their application to a wider range of germplasm will continue to open up new horizons for the collection, conservation, breeding and productivity of coconut.

Intact coconuts were germinated in situ and compared with excised zygotic embryos germinated in vitro. The growth of the embryonic tissue and their fatty acid compositions were measured. Haustoria, plumules and radicles of coconuts germinated in situ grew continuously and proportionately throughout the 120 d experiment with haustauria increasing to 45 g x nut(-1) and weighing 4-5-fold more than the other two tissues. The plumules and radicles of the seedlings cultured in vitro also grew continuously but the haustoria grew sporadically between 15 d and 75 d in culture and, at 250 mg x nut(-1) after 75 d, were smaller than the other two tissues. All the tissues of the nuts grown in situ contained significant amounts of lauric acid, the acid characteristic of coconut oil, as well as longer chain saturated and unsaturated fatty acids. The content of medium and long chain fatty acids increased in all growing tissues as the experiment proceeded, especially the haustorium which contained 24-35% of its fatty acid as lauric acid; the fat content of solid endosperm reduced during this period. Seedlings grown in vitro, on the other hand, failed to accumulate lauric acid in any of their tissues (haustorium contained 6-11% of its fatty acid as lauric acid). The results may have implications for the design of growth media for growing zygotic and somatic cultures of coconut and may provide a marker for successful germination.

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