Page 167 - PC2019 Program & Proceedings

PLANT CANADA 2019

S119. Mechanical role of callose plugs in pollen tubes
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Kapoor, K. ; A. Geitmann
McGill University

Pollen tube growth and gametic fusion are two fundamental processes that result in successful fertilization
and are crucial determinants of seed yield. Pollen tubes are fast growing cellular protuberances that
function to deliver sperm cells to female gametophyte. They are an ideal model to study plant cellular
morphogenesis, polar growth and cellular signaling. A growing pollen tube is exposed to different types
of stresses such as turgor induced tension stresses in the cell wall and compressive stresses exerted by the
growth matrix. Pollen tubes display a characteristic deposition of callose in the form of plugs that separate
the active portion of the pollen tube cytoplasm from the degenerating segments. Callose (ß-1,3 glucan) is
a polysaccharide in plant cell walls that is synthesized and accumulated at the outer surface of the plasma
membrane by callose synthase – a membrane localized enzyme. It is abundantly present in pollen grains,
pollen tube cell walls and callose plugs and must therefore have an important role for their specific
functions. My research explores the formation and the mechanical role of callose plugs. To understand the
mechanical properties of callose as a material, I perform mechanical assays to determine the correlation
between turgor pressure and callose abundance in the pollen tube cell wall. GFP tagging of callose
synthase enzyme will also provide insight into the molecular mechanism governing callose plug
formation

Karuna Kapoor (karuna.kapoor@mail.mcgill.ca)

S120. DONGLE and DAD-LIKE LIPASE2 enriched sites create organelle interaction hubs
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Lobbezoo, M. ; N. Mathur; J. Mathur
University of Guelph

Lipases hydrolyze lipids and help maintain cellular homeostasis and defense responses in plants.
Phospholipases A1 (PLA1) act on the sn-1 position of glycolipids to release lyso-lipids and free fatty
acids (FFA) and trigger the jasmonic acid biosynthesis pathway. While biochemical activity in the
pathway spans chloroplasts, peroxisomes, the endoplasmic reticulum (ER) and oil-bodies (OB) the
physical interactions between these organelles have not been observed in living cells. We have
investigated organelle interactions using fluorescent protein fusions of the phospholipases DONGLE
(DGL) and DAD-LIKE LIPASE2 (DALL2). Both proteins localized to the chloroplast envelope as
patches of variable size. While an earlier study had concluded additional localization of DGL on OB this
was not confirmed. Nevertheless, OB numbers and their clustering around chloroplasts increased
considerably in wounded leaf cells and under these conditions OB often localized to DGL enriched
patches. OB also associated with DGL-rich vesicles released from injured chloroplasts. Further
observations using ER-targeted fluorescent proteins showed the ER mesh interspersed with OB and OB-
peroxisome clusters and also showed the convergence of ER tubules to the lipase-enriched regions on the
chloroplasts. Our observations strongly suggest that during the early stages of plant defense response the
generation of signaling molecules such as FFA and lyso-lipids at lipase enriched regions of chloroplasts
creates subcellular hubs of increased physical interactions between the ER, OB and peroxisomes.

Mariann Lobbezoo (mlobbezo@uoguelph.ca)

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