Postdoctoral Fellow, University of California, Davis
Environmental cues and the circadian clock regulate flowering and pollinator visits in Sunflower
As sessile organisms, plants face many challenges including an ever-changing environment and numerous barriers to pollination. To overcome such barriers, many angiosperms employ insect pollination, which is also subject to daily and seasonal changes. Most organisms use their internal circadian clock to synchronise their biological processes to daily environmental changes. In plant-pollinator interactions, this leads to an intricate balancing act between the plant clock, pollinator clock, and the environment. Here we investigate how environmental cues and the plant clock co-ordinate flowering with pollinator visits. Sunflower is a well-studied model species for plant-pollinator interactions and more recently has been used to investigate the circadian regulation of heliotropism. This regulation plays an important role in the uniform easterly orientation of blooming sunflower heads. We have shown that early in the morning east-facing sunflowers are more attractive to pollinators than west-facing flowers, which is at least in part due to the warmer morning temperatures of east-facing flowers. Further investigations revealed that under constant environmental conditions the circadian clock generates 24 hr rhythms in floret maturation and pollen dehiscence, consistent with the release of pollen a few hours after dawn in field-grown plants. However, this clock-regulated process is also modulated by the environment and we have found that volatile emissions and pollen release occurs earlier in the day in east-facing than west-facing flowers in the field. This difference in phase may help explain the preference of pollinators for east-facing inflorescences in the morning. Growth chamber and field experiments suggest the clock and temperature co-ordinately influence the rate of anther filament and style elongation to fine-tune the timing of pollen release. Taken together, our findings point to a central role for the coordination of the circadian clock and environmental cues in regulating flowering and thereby controlling the precise timing of pollination of these complex inflorescences.
Abstract: Decades of observation in natural plant populations have revealed pervasive phenotypic selection for early flowering onset. This consistent pattern seems at odds with life-history theory, which predicts stabilizing selection on age and size at reproduction. Why is selection for later flowering rare? Moreover, extensive evidence demonstrates that flowering time can and does evolve. What maintains ongoing directional selection for early flowering? Several non-mutually exclusive processes can help to reconcile the apparent paradox of selection for early flowering. We outline four: selection through other fitness components may counter observed fecundity selection for early flowering; asymmetry in the flowering-time-fitness function may make selection for later flowering hard to detect; flowering time and fitness may be condition-dependent; and selection on flowering duration is largely unaccounted for. In this Viewpoint, we develop these four mechanisms, and highlight areas where further study will improve our understanding of flowering-time evolution.
Pub.: 19 Apr '17, Pinned: 15 Jun '17
Abstract: • The discrepancy between observed flower visitors and those predicted based on floral phenotype has often cast doubt on the pollination syndrome concept. Here we show that this paradox may be alleviated by gaining a better knowledge of the contributions of different flower visitors to pollination and the effects of floral traits that cannot be readily perceived by humans in Adenophora triphylla var. japonica. The blue, bell-shaped and pendent flowers of A. triphylla appear to fit a bee pollination syndrome. In contrast to this expectation, recent studies show that these flowers are frequented by nocturnal moths. • We compared the flower-visitor fauna, their visitation frequency and their relative contributions to seed set between day and night in two field populations of A. triphylla in Japan. We also determined the floral traits associated with temporal changes in the visitor assemblage, i.e., the timing of anthesis, the timing of changes in the sexual phase and the diel pattern of nectar production. • While A. triphylla flowers were visited by both diurnal and nocturnal insects, the results from pollination experiments demonstrate that their primary pollinators are nocturnal settling moths. Moreover, the flowers opened just after sunset, changed from staminate to pistillate phase in successive evenings and produced nectar only during the night, which all conform to the activity of nocturnal/crepuscular moths. • Our study illustrates that the tradition of stereotyping the pollinators of a flower based on its appearance can be misleading and that it should be improved with empirical evidence of pollination performance and sufficient trait matching. This article is protected by copyright. All rights reserved.
Pub.: 12 May '17, Pinned: 15 Jun '17
Abstract: Authors: John Love ; Sean W. Graham ; Judith A. Irwin ; Paul A. Ashton ; Francois Bretagnolle ; Richard J. Abbott Article URL: http://www.tandfonline.com/doi/full/10.1080/17550874.2016.1244576?ai=31h&af=R Citation: Plant Ecology & Diversity Publication Date: 2016-10-18T06:08:26Z Journal: Plant Ecology & Diversity
Pub.: 18 Oct '16, Pinned: 15 Jun '17
Abstract: Global food security, particularly crop fertilization and yield production, is threatened by heat waves that are projected to increase in frequency and magnitude with climate change. Effects of heat stress on the fertilization of insect-pollinated plants are not well understood, but experiments conducted primarily in self-pollinated crops, such as wheat, show that transfer of fertile pollen may recover yield following stress. We hypothesized that in the partially pollinator-dependent crop, faba bean (Vicia faba L.), insect pollination would elicit similar yield recovery following heat stress. We exposed potted faba bean plants to heat stress for 5 days during floral development and anthesis. Temperature treatments were representative of heat waves projected in the UK for the period 2021-2050 and onwards. Following temperature treatments, plants were distributed in flight cages and either pollinated by domesticated Bombus terrestris colonies or received no insect pollination. Yield loss due to heat stress at 30 °C was greater in plants excluded from pollinators (15%) compared to those with bumblebee pollination (2.5%). Thus, the pollinator dependency of faba bean yield was 16% at control temperatures (18-26 °C) and extreme stress (34 °C), but was 53% following intermediate heat stress at 30 °C. These findings provide the first evidence that the pollinator dependency of crops can be modified by heat stress, and suggest that insect pollination may become more important in crop production as the probability of heat waves increases.
Pub.: 19 Mar '16, Pinned: 15 Jun '17
Abstract: Experiments were conducted over 2 years to quantify the response of faba bean (Vicia faba L.) to heat stress. Potted winter faba bean plants (cv. Wizard) were exposed to temperature treatments (18/10; 22/14; 26/18; 30/22; 34/26 °C day/night) for 5 days during floral development and anthesis. Developmental stages of all flowers were scored prior to stress, plants were grown in exclusion from insect pollinators to prevent pollen movement between flowers, and yield was harvested at an individual pod scale, enabling effects of heat stress to be investigated at a high resolution. Susceptibility to stress differed between floral stages; flowers were most affected during initial green‐bud stages. Yield and pollen germination of flowers present before stress showed threshold relationships to stress, with lethal temperatures (t50) ˜28 °C and ~32 °C, while whole plant yield showed a linear negative relationship to stress with high plasticity in yield allocation, such that yield lost at lower nodes was partially compensated at higher nodal positions. Faba bean has many beneficial attributes for sustainable modern cropping systems but these results suggest that yield will be limited by projected climate change, necessitating the development of heat tolerant cultivars, or improved resilience by other mechanisms such as earlier flowering times.
Pub.: 21 Mar '16, Pinned: 15 Jun '17
Abstract: Young sunflower plants track the Sun from east to west during the day and then reorient during the night to face east in anticipation of dawn. In contrast, mature plants cease movement with their flower heads facing east. We show that circadian regulation of directional growth pathways accounts for both phenomena and leads to increased vegetative biomass and enhanced pollinator visits to flowers. Solar tracking movements are driven by antiphasic patterns of elongation on the east and west sides of the stem. Genes implicated in control of phototropic growth, but not clock genes, are differentially expressed on the opposite sides of solar tracking stems. Thus, interactions between environmental response pathways and the internal circadian oscillator coordinate physiological processes with predictable changes in the environment to influence growth and reproduction.
Pub.: 06 Aug '16, Pinned: 08 Jun '17
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