A mathematical model explores the contributions of bending and stretching forces to shoot gravitropism in Arabidopsis

Plant shoot gravitropism is a complex phenomenon resulting from gravity sensing, curvature sensing (proprioception), the ability to uphold self-weight and growth. Although recent data analysis and modelling have revealed the detailed morphology of shoot bending, the relative contribution of bending force (derived from the gravi-proprioceptive response) and stretching force (derived from shoot axial growth) behind gravitropism remains poorly understood. To address this gap, we combined morphological data with a theoretical model to analyze shoot bending in wild-type and lazy1-like 1 mutant Arabidopsis thaliana. Using data from actual bending events, we searched for model parameters that minimized discrepancies between the data and mathematical model. The resulting model suggests that both the bending force and the stretching force differ significantly between the wild type and mutant. We discuss the implications of the mechanical forces associated with differential cell growth and present a plausible mechanical explanation of shoot gravitropism.

Effect of Shoot Bending and Fruit Thinning on Productivity of Guava

The study was carried out at the Germplasm Centre of Fruit Tree Improvement Programme (GPC-FTIP), Bangladesh Agricultural University, Mymensingh during the period February, 2011 to March, 2012 to find out the effect of shoot bending and fruit thinning on productivity of guava. The treatments of the experiment were four varieties of guava viz., Swarupkathi, BAU piyara-5, Chiang Mai (round) and Chiang Mai (long) and six different management practices viz., (i) control (no shoot bending + no fruit thinning); (ii) shoot bending; (iii) 25% fruit thinning; (iv) 50% fruit thinning; (v) 75% fruit thinning and (vi) 100% fruit thinning. The ages of the plants were 4-5 years. Results revealed that the variety Chiang Mai (round) showed superiority over BAU piyara-5, Chiang Mai (long) and Swarupkathi in respect of fruit yield (15.63 kg/plant) and fruit retention (72.92%) during on-season but during off-season, Swarupkathi showed superiority over Chiang Mai (round), BAU piyara-5 and Chiang Mai (long) in case of number of flowers set per plant (127.44), number of fruits set per plant (75.28), fruit retention (88.66%) and yield (11.78 kg/plant). Different management practices had significant effect on all studied parameters in both seasons. Fifty percent fruit thinning treatment showed the highest fruit yield (20.46 kg/plant) and 75% fruit thinning treatment performed lowest fruit yield (10.06 kg/plant) during on-season but during off-season shoot bending performed highest fruit yield (13.50 kg/plant). Highest fruit retention in both seasons (on-season 89.28% and off-season 90.47%) was observed in 50% fruit thinning treatment. In case of combined effect of variety and different management practices, 50% fruit thinning treatment combined with Chiang Mai (round) produced highest yield (23.15 kg/plant) and fruit retention (92.72%) during on-season, but shoot bending treatment combined with Swarupkathi gave the highest yield (16.06 kg/plant) and 50% fruit thinning combined with Swarupkathi showed highest fruit retention (94.12%) during off-season.DOI: http://dx.doi.org/10.3329/jesnr.v5i2.14808 J. Environ. Sci. & Natural Resources, 5(2): 167-172 2012