|Males Flower Earlier But is it Due to Leaf Phosphate?
Author* and Supervisor names
*CONTACT ADDRESS: --------------, Department of Biology PO Box 373, University of York, Heslington, Yo10 5YW Email: --------------
Flowering time is critical to the reproductive success of a plant and is influenced by many factors, including shoot phosphate concentration. The link between shoot phosphate and flowering time was established in Holcus lanatus populations that exhibit a polymorphism for phosphate nutrition. Plants with the dominant allele for this polymorphism have a greater phosphate concentration and flower earlier than plants with the recessive allele (Meharg et al, 1993).
Phosphate has also been implicated in determining the flowering times in the pho mutants of Arabidopsis thaliana and in Silene dioica. Pho 2 which has high shoot P concentrations, flowers two days earlier than wild type plants (Wright, 1999). Hemborg and Karlsson (1999) showed that males of Silene dioica flowered earlier than females. This trait is typical of many dioecious plants. Intriguingly, although there were no differences in biomass or N content between the two sexes, males had a greater P concentration than females.
The present field study asks three specific questions:
1. Do males flower earlier than females in Silene dioica?
2. Do males have greater leaf phosphate concentrations than females?
3. Is leaf phosphate related to flowering time?
60 plants were marked along a transect.
Phosphate analysis was done on the leaf samples.
Time of first flowering was recorded. First flowering was taken as first fully opened flower.
1. Do Males Flower earlier than females?
Figure 3 demonstrates that males flower earlier than females and that the first flowering time of the males is spread over a longer time period than the females.
2. Do Males have a great leaf phosphate concentration than females?
Figure 3 shows that males do not have a greater leaf [P] at flowering.
In the weeks leading up to flowering there is no difference in leaf [P] either (data not shown).
3. Is leaf Phosphate related to flowering time?
Figures 4 and 5 show that there is a difference in the relationship between leaf phosphate and flowering between males and females.
However, it is not conclusive that there is a true relationship between flowering time and leaf phosphate concentration in either males or females.
Fig 2. First flowering time of male and female Silene dioica plants (One-way ANOVA F1,44 = 6.73, P = 0.01). Time taken as time after first plant flowered.
Fig 3. [P] at time of flowering for males and females of Silene dioica (one-way ANOVA F1,46 = 0.732, P = 0.397).
Fig. 4. Phosphate concentration in leaves at flowering vs flowering time fir male Silene dioica plants (linear regression F 1,24 = 3.65, P = 0.068).
Fig. 5. Phosphate concentration in leaves at flowering time vs flowering time for female Silene dioica plants (linear regression F 1,20 = 4.65, P = 0.043).
Male Silene dioica flower
Female Silene dioica flower
This study has demonstrated so far that:
Males flower earlier than females in the field.
Males and females do not have a different leaf phosphate concentration.
However, there is a different relationship between leaf phosphate concentration and flowering time.
The positive relationship between flowering time and leaf phosphate is the opposite of the expected result.
Further exploration of data is needed to gain a fuller understanding as to the relationship between flowering time and leaf phosphate concentration in the different sexes.
Phosphate concentrations of whole plant biomass would be required to gain a greater understanding of its relationship with flowering time.
Lab based investigations on both Arabidopsis thaliana and Silene dioica will hopefully lead to a greater understanding of the affect phosphate has on flowering.
1. Hemborg A.M., P.S. Karlsson (1999). Sexual differences in biomass and nutrient allocation of first-year Silene dioica plants. Oecologia 118:453-460
2. Meharg A.A., Q.J. Cumbes, M.R. Macnair (1993). Pre-adaption of Yorkshire Fog, Holcus lanatus L. (Poaceae) to arsenate tolerance. Evolution 47:313-316
3. Wright W. (1999). Reproductive biomass and mycorrhizal colonisation in grass populations polymorphic for phosphate uptake kinetics. PhD thesis, Univ. York .
This work was funded by the bbsrc
Thanks to xxxxxxxxxxxxxxxx for helping with the collection of data in the field.