4 DISCUSSION
The anther development in wheat fallows a pattern similar to other
members of Poaceae family, including Brachypodium
distachyon (Sharma et al., 2015) and rice (Zhang et al., 2006).
Resemblances also exist in Arabidopsis thaliana (Chang et al.,
2011) but some distinct differences were recorded in wheat anther
development. The critical step in the anther development is the balance
of cell sizes (width, length and depth) and the cell counts of EPI, EN,
SPL, ML, TA, PMC, MP and PG cells. Therefore, we investigated the
effects of T. laevis and T. controversa on above cell
sizes and number on comparison with control anthers.
4.1 The timeline of cell
development of normal wheat anther
In this study, we firstly construct the timeline of wheat anther
development using confocal microscopy. The AR cells appear from L2 layer
of anthers < 150 µm and differentiate into EN, SPL and PMC
cells of anthers. In this range, vascular tissues developed more
clearly. The SPL cells differentiate into ML and TA almost in 400 µm
long anthers. PMC cells differentiate into Tds almost in 700 µm anthers,
where ML start to be wrinkled between TA and EN cells and disappear
almost in 1100 µm anthers. Tds start to change into MP almost from
720-1000 µm anthers. Here ML is scarcely present, and TA is at its most
swollen and largest size. However, near to 1200 µm, MP become vacuolate
towards the TA walls. An exine layer start to develop on the MP and TA
began to reduce in size (Browne et al., 2018). At 1300 µm, TA cells
disappear, and microspore grow large and began to change in PG cells. At
2300 µm, mature PG formed and which are starch filled. EPI cells at
stomium start to degrade, causing locules to open and PG start to be
released (Figure 1 ). RAFTIN1 and TaMYB80 play a
crucial role in TA development and TA program cell death (Gao et al.,
2013; Wang et al., 2003; Murray et al., 2003; Millar et al., 2005). We
approved the anther timeline by analyzing the expression of TA
development and TA program cell death in different anther length.
Results showed that the expression of RAFTAN1 was high in 200-900
µm anther compared to other sized anthers. While, TaMYB80 showed
maximum expression in 1100-1300 µm anthers. The expression results
suggested that TA start to develop from 400 µm anthers and almost
disappear in 1300 µm anthers (Figure S1 ). Confocal results
showed that PMC cells were surrounded by three somatic cell layers:
namely EPI, EN and SPL from interior to outside (Figure 2B ).
Except EPI, the three inner cells were differentiated after mitotic
division in AR cells. Hence, earliest and most important, steps in
anther development are the production of AR cells. The final structure
results in the PMC enclosed by a serious of somatic cells, which are EN,
SPL and EPI (Figure 2B ). Finally, after meiosis PMC cells
differentiate into PG almost from 1300 to 2300 µm, which released from
pollen sac by opening the stomium (Figure 2I ). However,
according to Browne et al. (2018), AR cells generated primary
parietal cells (PPC) and primary sporogenous cells (PSC) after mitosis.
Then PPC divide into EN and ML and PSC divide into PMC cells, which
produce Tds. In our results, AR cells directly differentiate into EN,
SPL and PMC cells and then SPL cells divide into ML and TA and PMC cells
divide into Tds that differentiate into MP and PG in short time.
Moreover, the difference in wheat anther development was noted from
model plant, Arabidopsis thaliana (Chang et al., 2011). However,
according to Zhang and Wilson (2009) the EN, SPL and PMC cells
differentiate from AR cells then it differentiate into other cells.