SALINITY STRESS ON THE PHYTOHORMONE CONTENT AND PHYSIOLOGICAL RESPONSE OF MACROALGA Gracilariopsis lemaneiformis  

Both low and high salinity <app:ds:salinity> could inhibit the growth of marine red algae Gracilariopsis lemaneiformis. Under low salinity <app:ds:salinity> conditions of 10‰, the IAA content was significantly lower than the control, but all stress phytohormones, including ABA, JA, SA and RA increased. The cell Pit connections were destroyed and intracellular floridean starch content decreased. The content of Na⁺, K⁺, Ca²⁺, Mg²⁺ showed no significant change. The content of phycoerythrin, phycocyanin and chlorophyll decreased to a certain degree in the initial phase and then rebounded in the later phase. The proline content decreased by 21.11%, while those of mannitol increased by 19.61%.

While under high salinity <app:ds:salinity> stress of 35‰, the IAA content decreased slightly and the content of ABA and JA showed significant increased. The chromatoplast <app:ds:chromatoplast> were destroyed and more salt particles accumulate <app:ds:accumulate>d. The Na⁺ content rise and the K⁺ and Ca²⁺ content dropped. The MDA content increased rapidly in the initial phase with stresses, but SOD and POD activity increased significantly in the later phase to clear the reactive oxygen species (ROS). Salinity stress contributes to the decline in optimal quantum yield (F_v/F_m). And all three kinds of photosynthetic pigments have declined, and dropped to an average of 71.80% of the control group.

It can conclude that salt stress caused the phytohormone change of algae, and then cause other physiological response of Gp. lemaneiformis.