Unidirectional movement of cellulose synthase complexes in Arabidopsis seed coat epidermal cells deposit cellulose involved in mucilage extrusion, adherence, and ray formation.

Cellulose synthase5 (CESA5) synthesizes cellulose necessary for seed mucilage adherence to seed coat epidermal cells of Arabidopsis (Arabidopsis thaliana). The involvement of additional CESA proteins in this process and details concerning the manner in which cellulose is deposited in the mucilage pocket are unknown. Here, we show that both CESA3 and CESA10 are highly expressed in this cell type at the time of mucilage synthesis and localize to the plasma membrane adjacent to the mucilage pocket. The isoxaben resistant1-1 and isoxaben resistant1-2 mutants affecting CESA3 show defects consistent with altered mucilage cellulose biosynthesis. CESA3 can interact with CESA5 in vitro, and green fluorescent protein-tagged CESA5, CESA3, and CESA10 proteins move in a linear, unidirectional fashion around the cytoplasmic column of the cell, parallel with the surface of the seed, in a pattern similar to that of cortical microtubules. Consistent with this movement, cytological evidence suggests that the mucilage is coiled around the columella and unwinds during mucilage extrusion to form a linear ray. Mutations in CESA5 and CESA3 affect the speed of mucilage extrusion and mucilage adherence. These findings imply that cellulose fibrils are synthesized in an ordered helical array around the columella, providing a distinct structure to the mucilage that is important for both mucilage extrusion and adherence.

Factors affecting podophyllotoxin yield in the ex situ grown Podophyllum hexandrum, an endangered alpine native of the western Himalayas.

This study reports an appreciable yield of podophyllotoxin (PDT) in P. hexandrum plants grown ex situ under polyhouse conditions of a temperate locale. The PDT content of below-ground parts was affected by both plant age and growth period. However, only the effect of plant age on PDT content was significant. Thus, the highest amounts of PDT were recorded in the below-ground parts of 2-year-old plants harvested during the late-growth period (LGP). High total soluble sugars in the below-ground parts during the early growth period (EGP) and the highest nitrate and nitrate reductase in the leaves of 2-year-old plants during the peak-growth period (PGP) indicated higher mobilization and assimilation of starch and nitrate. Probably the surplus carbon and nitrogen gained during the PGP were diverted from aerial parts to below-ground parts during the LGP and in turn contributed to the synthesis of higher amounts of PDT. This study shows that commercial cultivation of P. hexandrum is possible under ex situ temperate conditions.

An efficient method of propagation of Podophyllum hexandrum: an endangered medicinal plant of the Western Himalayas under ex situ conditions.

This study shows an effective but simple method of conserving characterized populations and elite clones through vegetative propagation and genetic diversity through seeds in Podophyllum hexandrum (family Berberidaceae). Seed dormancy has been considered to be a major constraint in these seeds and most of the earlier reports recommended dormancy-breaking pretreatments such as chilling, gibberellic acid (GA(3)), etc. However, seeds of the 14 accessions that we tested exhibited no dormancy and hence did not require any pretreatments. Besides accession, collection of seeds with high moisture content could be one of the reasons for lack of dormancy. Thus, we propose germination of seeds (while they still retained moisture) in sand at 25 degrees C for high and reproducible results within a shorter period of time compared with earlier reports. Hypocotyl dormancy is known to considerably delay plant establishment and hence en masse propagation by preventing the emergence of functional leaves for up to 11-12 months. Manual removal of cotyledonary leaves, being labor and time intensive, is not a feasible method for large-scale seedling establishment. However, in this study, we showed that GA(3) at 200 ppm can alleviate hypocotyl dormancy besides reducing the time taken for true or functional leaf emergence. Treatment of cotyledonary leaves of 1 week-old-seedlings with 200 ppm GA(3 )resulted in true or functional leaf emergence within 7 days, and the resultant plants were also more vigorous than the ones obtained from manual removal of cotyledonary leaves. The study helped advance the establishment of seedlings by one growing season (almost 1 year).

Temperature-dependent growth and emergence of functional leaves: an adaptive mechanism in the seedlings of the western Himalayan plant Podophyllum hexandrum.

As an adaptive mechanism, hypocotyl dormancy delays emergence of functional leaf until favorable season of growth in Podophyllum hexandrum, an endangered medicinal plant of the western Himalayas. However, upon exposure of the freshly germinated seedlings to favorable temperature (25 degrees C), functional leaves emerged within 20 days. Therefore, we examined regulation mechanisms of growth and development of this alpine plant by temperature under laboratory conditions. The seedlings were exposed to (1) 25 degrees C (temperature prevailing at the time of maximum vegetative growth), (2) 4 degrees C (mean temperature at the onset of winter in its natural habitat), and (3) 10 degrees C (an intermediate temperature). Slackened growth at 4 degrees C was followed by senescence of aerial parts and quiescence of roots and predetermined leaf primordia. Rapid development of leaf primordia at 25 degrees C was associated with increased starch hydrolysis. This was evident from higher alpha-amylase activity and reducing sugars. These parameters decreased on sudden exposure to 4 degrees C. In contrast, the roots (perennating organs) showed a slight increase (1.36-fold) in alpha-amylase activity. Growth and development in seedlings growing at 10 degrees C (temperature less adverse than 4 degrees C) were comparatively faster. The content of reducing sugars and alpha-amylase activity were also higher in all the seedling parts at 10 degrees C as compared to 4 degrees C. This indicated larger requirements for sugar by the seedlings at 10 degrees C. Irrespective of temperature, maximum changes in nitrate and nitrate reductase occurred during the initial 10 days, i.e., when the readily available form of sugars (reducing sugar) was highest. This indicated that a temperature-dependent availability of carbon, but not temperature itself, was an important regulator of uptake and reduction of nitrogen.