Plant growth – resource or strategy limited: insights from responses to gibberellin

Abstract

We used exogenous application of a phytohormone (gibberellin GA3, ‘GA’) to test the hypothesis that common perennial grasses may not be growing at all times to the limit of resource availability. Plants were taken from the field in winter, and again in summer and their responses to GA assessed under standard conditions, indoors, to reveal their ‘potential’ for growth at different times. Time of year, and associated developmental state, had a major impact on the capacity of plants to respond to exogenous GA, and less so their current growing conditions, temperature and N availability, during measurement. A major increase in dry matter (DM) production in winter‐derived plants took place at both low and high N, with no evidence of a reduction in N content in tissues. That ryegrass plant growth can be stimulated, without externally adding resources, supports the hypothesis there is an element of internal control in how plants respond to ‘signals’ in their environment, that might be manipulated. This offers prospects for reducing environmental impacts (leaching, N2O) compared with obtaining the same yield increase by adding fertilizer N in early season. Responses to exogenous GA were detected (as significant) but far smaller in summer‐derived plants. Molecular mechanisms of detection of N resource signals, developmental triggers and the role of endogenous gibberellin need to be unravelled to assess scope for breeding ryegrass germplasm to better match demands for increased production with greater resource‐use efficiency.

Effects of forage type and gibberellic acid on nitrate leaching losses

“…In contrast to these studies, Parsons et al . () found a major increase in DM production in winter‐derived plants at both low and high N, with no evidence of a reduction in N content of tissues. This suggested that the extra growth increased N uptake from the soil environment.…”

“…Additionally, NO À 3 leaching has been linked to winter daily N uptake by pasture (Malcolm et al, 2014). To further enhance plant uptake of N and potentially reduce the risk of N leaching, the use of gibberellic acid (GA), a plant growth stimulant, has been proposed (Parsons et al, 2013). Gibberellic acid is responsible for stem elongation and leaf expansion in plants (Matthew et al, 2009).…”

Leaf Length Variation in Perennial Forage Grasses

“…It is not surprising to find different QTL for leaf length parameters in the reproductive stage in spring (even very early in floral development) and in the vegetative stage in autumn. Indeed, the limitations to leaf growth in the two stages are not the same [32]. Another source of variability arises from the way in which the measurements of leaf length are taken.…”

“…Growth rate increases markedly following flower induction and before any visible stem elongation ( Figure 2) [28][29][30]. This change in leaf growth rate seems to be due to an increase in cell division which could be related to environmental regulation of the gibberellins pathway [31][32][33]. Consequently, for a given genotype, leaf length varies greatly depending on whether the leaf grows on an axis which has been induced for flowering or not.…”

Comparison of signaling interactions determining annual and perennial plant growth in response to low temperature

“…The growth response in grasses to temperature is regulated by GA. Growth of perennial ryegrass increases after GA application, even without nitrogen addition, but a positive interaction was found with nitrogen supply ( Ball et al, 2012 ; Parsons et al, 2013 ). Importantly, plants collected from a pasture in winter showed a stronger response to GA than plants collected in summer ( Ball et al, 2012 ), demonstrating that seasonal factors determine the capacity for growth.…”