Abstract
BackgroundThe calcifying siphonalean green alga, Halimeda macroloba is abundant on coral reefs and is important in the production of calcium carbonate sediments. The process by which new green segments are formed over-night is revealed here for the first time.Methodology/Principal FindingsGrowth of new segments was visualised by epifluorescence and confocal microscopy and by pulse amplitude modulation (PAM) fluorimetry. Apical colourless proto-segments were initiated on day 1, and formed a loose network of non-calcified, non-septate filaments, containing no chloroplasts. Rapid greening was initiated at dusk by i) the mass movement of chloroplasts into these filaments from the parent segment and ii) the growth of new filaments containing chloroplasts. Greening was usually complete in 3–5 h and certainly before dawn on day 2 when the first signs of calcification were apparent. Mass chloroplast movement took place at a rate of ∼0.65 µm/s. Photosynthetic yield and rate remained low for a period of 1 to several hours, indicating that the chloroplasts were made de novo. Use of the inhibitors colchicine and cytochalasin d indicated that the movement process is dependent on both microtubules and microfilaments.SignificanceThis unusual process involves the mass movement of chloroplasts at a high rate into new segments during the night and rapid calcification on the following day and may be an adaptation to minimise the impact of herbivorous activity.
Highlights
Calcifying siphonalean green algae in the genus Halimeda are abundant on coral reefs around the world [1] and are important in the sequestration of carbon from the atmosphere [1,2]
The siphonalean green alga Halimeda has been studied for many years because of its special features in terms of calcification [3,15,16,17,18] and circadian chloroplast movement [21,22]
The mechanisms involved in new segment formation have hitherto been unknown and our study shows for the first time that segment formation involves a complex series of events, whose further study could be a very valuable tool in plant cell research
Summary
Calcifying siphonalean green algae in the genus Halimeda are abundant on coral reefs around the world [1] and are important in the sequestration of carbon from the atmosphere [1,2]. Bundles of the aragonite crystals from dead Halimeda plants are an abundant source for the fine-grained sediments on many coral reefs [1]. As in all members of the Order Siphonales, the thallus is formed from branching filaments, which have few septa and the plant is coenocytic. The cortical radial filaments branch extensively and fuse at the apices of branches to form a closed surface [3]; beneath this closed surface there is free space between the filaments known as the inter-utricular space. The calcifying siphonalean green alga, Halimeda macroloba is abundant on coral reefs and is important in the production of calcium carbonate sediments. The process by which new green segments are formed over-night is revealed here for the first time
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
