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

Abstract

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.

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

“…Hence, most alpine plants exhibit opportunistic growth behavior not only to complete their time-bound growth targets, but also to store ample reserves of primary metabolites much before the onset of harsh winters. Since P. hexandrum also exhibits such behavior, it attains maximum vegetative growth during the summers, the time when the growth-favoring environmental temperature (i.e., about 25°C) prevails [6]. Even under the milder temperate climate of Palampur where a favorable temperature regime prevails for longer duration, P. hexandrum exhibits this behavior.…”

“…2b-g, 3). Earlier, Kushwaha et al [6] showed that senescence of aerial green photosynthetic parts was initiated at temperatures below 15°C, and metabolites were mobilized to the below-ground parts. This enabled the plants to survive the low winter temperatures (4°C or lower) under in situ conditions.…”

“…The plant avoids, rather than tolerates its harsh environmental conditions by strictly synchronizing its growth with seasonal variations in temperature [6]. It has also been shown that P. hexandrum can be grown ex situ at lower temperate altitudes [7].…”

Transcriptome sequencing of rhizome tissue of Sinopodophyllum hexandrum at two temperatures

“…Like other alpine plant species [ 6 ], S. hexandrum has been reported to be sensitive to high temperature [ 7 ]. S. hexandrum consumed more starch at 25°C as compared to at 10°C leading to poor root growth at the former temperature [ 7 ]. Also, the rate of photosynthesis was reported to be lower at 30°C as compared to at 20°C.…”

Application of betaine improves solution uptake and in vitro shoot multiplication in tea

“…To this, 10 ml de-ionized water was added along with ammonia solution (1:1) until a yellow colour developed. Absorbance was read at 420 nm and the level of nitrate determined using spectrophotometer (Hitachi, Japan) against a standard curve prepared with KNO 3 (Kushwaha et al 2008).…”