EFFECTS OF ETHYLENE ON TETRASPOROGENESIS IN PTEROCLADIELLA CAPILLACEA (RHODOPHYTA) 1 PilarGarcı´a-Jime´nez 2 and Rafael R. Robaina Departamento de Biologı ´a. Facultad de Ciencias del Mar. Universidad of Las Palmas de Gran Canaria. E-35017 Las Palmas de Gran Canaria, Canary Islands, Spain The effects of ethylene (C 2 H 4 ) on tetrasporogene- sis of the red seaweed Pterocladiella capillacea (S. G. Gmelin) Bornet were investigated. Ethylene is a gas- eous hormone that is involved in a variety of physio- logical processes (e.g., flowering, fruit abscission) in higher plants. To study the effects of ethylene on the reproduction of the red seaweed P. capillacea, immature tetrasporophytic thalli were exposed to a flow of ethylene for different time periods. Maxi- mum maturation of tetrasporangia was observed at 7 d in thalli exposed to ethylene for 15 min. This maturation was accompanied by a significant increase in the free fraction of putrescine (Put) and a 5-fold increase in the level of total RNA. These changes were specifically due to ethylene since they were blocked by the presence of the ethylene per- ception inhibitor silver thiosulphate (STS). More- over, P. capillacea was determined to produce ethylene at a rate of 1.12 ± 0.06 nmol ethylene Æ h )1 Æ g )1 fresh weight (fwt) with specific activities for 1-aminocyclopropane-1-acrylic acid (ACC) synthase of 11.21 ± 1.19 nmol ethylene Æ h )1 Æ mg )1 protein and for ACC oxidase (ACO) of 7.12 ± 0.11 nmol ethylene Æ h )1 Æ mg )1 protein. We conclude that eth- ylene may indeed be a physiological regulator of tet- rasporogenesis in this red seaweed. Key index words: ACC oxidase; ACC synthase; ethylene; polyamines; Pterocladiella; Rhodophyta; seaweed Abbreviations: ACC, 1-aminocyclopropane-1-acrylic acid; ACS, ACC synthase; ACO, ACC oxidase; PAs, polyamines; Put, putrescine; STS, silver thiosul- phate; Spd, spermidine; Spm, spermine Ethylene is a senescence-promoting gaseous hor- mone that in higher plants favors ripening and fruit abscission (Bregoli et al. 2002, Torrigiani et al. 2004), as well as responses to stress such as wounding and pathogen attack (Abeles et al. 1992). Ethylene is synthesized by the conversion of S-adenosyl methionine (SAM) into ACC by the enzyme ACC synthase (ACS). ACC is converted to ethylene by ACO. The effects of ethylene on algae in general are poorly characterized. It is known that the green alga Ulva intestinalis produces ethylene, and the use of ethephon (an ethylene-releasing agent) provoked the loss of chl (Plettner et al. 2005). In the unicellu- lar alga Acetabularia, cap formation was altered in a manner dependent on the timing of application of ethylene (Vanden Driessche et al. 1998). In contrast, the growth, development, and repro- duction of red seaweeds are known to be controlled by polyamines (PAs). Spermidine (Spd), spermine (Spm), and their diamine obligate precursor Put are small aliphatic polyamines that are ubiquitous in all plant cells. They have been labeled as a type of plant growth regulator or hormonal second mes- senger (Galston and Kaur-Sawhney 1990, Lee and Chu 1992, Tiburcio et al. 1993, Scoccianti et al. 2000, Tassoni et al. 2000). PAs stimulated cell division in sporelings of the red seaweed Grateloupia imbricata (as G. doryphora) such that they become organized cell masses in the presence of Put and Spd, and calli (disorganized cell masses) in the presence of Spm (Garcı ´a-Jime ´nez et al. 1998, Maria ´n et al. 2000). Other studies have monitored endogenous levels of PAs during matura- tion of reproductive structures. In the red seaweed Gracilaria cornea, the highest PA values were found in tissue from the early postfertilization stage and decreased as the cystocarp matured (Guzma ´n- Urio ´stegui et al. 2002). In G. imbricate, infertile axes (not showing cystocarps) of gametophyte thalli accu- mulated more PAs than those axes with cystocarps (Sacramento et al. 2004, 2007). In addition, maxi- mum activity of ornithine decarboxylase enzyme (ODC, EC.4.1.1.17), a key enzyme of synthesis of PAs, was also associated with infertile axes (Sacramento et al. 2004, 2007). Moreover the addition of exoge- nous Spm to in vitro cultures of Gracilaria and Grate- loupia showed an increase in the number of carposporangial cell lines and mature spores (Guzma ´n- Urio ´stegui et al. 2002, Sacramento et al. 2004, 2007). The gene encoding ODC (GiODC Accession number FJ223132) showed differential expression with fewer transcripts in apices of G. imbricata where cystocarps were present (Garcı ´a-Jime ´nez et al. 2009). 1 Received 20 June 2011. Accepted 3 November 2011. 2 Author for correspondence: e-mail pgarcia@dbio.ulpgc.es. J. Phycol. 48, 710–715 (2012) Ó 2012 Phycological Society of America DOI: 10.1111/j.1529-8817.2012.01156.x 710