Poster: Tropisms
Abs #
662: Gravistimulation changes microtubule distribution in caulonemal filaments of Physcomitrella patens
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Presenter: |
Allen, Nina S. |
Authors | Chattaraj, Parna (A) Johannes, Eva (A) Allen, Nina S. (A) | | Affiliations: |
(A): North Carolina State University
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Dark grown caulonemal filaments of P. patens are negatively gravitropic and the tip growing apical cell perceives and responds to changes in the gravity vector. The tip cell contains amyloplasts that settle slightly in response to gravistimulation. In the tip growing cell of Ceratodon, Schwuchow et al (Protoplasma 1990,159:60-69) found that microtubule (MT) distribution changed over time after gravistimulation indicating that they have a prominent role in the observed growth response. The role of actin in gravireception and response of mosses is less clear, since actin depolymerization inhibits growth and therefore the graviresponse. We have investigated the role of MTs in the gravitropic response of P.patens using immunofluorescence and confocal microscopy. In these cells, phototropic responses override gravitropic responses and hence we did all experiments in darkness and/or dim green light. In six day old filaments, the MT fluorescence intensity increased markedly at 30 mins after a 90 degree turn and peaked at 1 hour. The MT depolymerizing agent, oryzalin delayed growth in both unstimulated and gravistimulated filaments accompanied by bulging and sometimes branching of the tip cell. In oryzalin treated filaments branching lead to establishment of one new graviresponsive growth point. The typical zonation pattern disappeared when MTs break up and once the zonation reappeared, the cells resumed growth and were graviresponsive again. In oryzalin treated filaments, the MT accumulation on the lower flank was also delayed and appeared 4 hours after gravistimulation. We conclude that microtubules are important for signal transduction and response in P. patens and their depolymerization leads to delayed growth and graviresponse. (Supported by NASA grant NAGW 4984.)
