Cronin Greg, Hay Mark E
Institute of Marine Sciences, University of North Carolina at Chapel Hill, 28557, Morehead City, NC, USA.
Oecologia. 1996 Feb;105(3):361-368. doi: 10.1007/BF00328739.
Within-plant variation in the concentration of secondary metabolites, nutritive value, toughness, and susceptibility to herbivory was assessed for the brown alga Dictyota ciliolata. When young apices and older tissue from the same plant were offered in equal abundance to the herbivorous amphipod Ampithoe longimana and the sea urchin Arbacia punctulata, young apices were consumed about 2 times more than older tissue. Compared to young apices, the less preferred older tissue had a less palatable lipophilic extract, significantly higher concentrations of two secondary metabolites (another secondary metabolite did not differ significantly), 33% more soluble protein, and was 233% tougher. Higher levels of chemical defenses in older tissues, and not tissue toughness or nutritive value, appear to be responsible for the preference of Ampithoe longimana for young apices. The pattern of lower levels of chemical defenses in young than older tissues of D. ciliolata is the opposite of the pattern observed in coenocytic seaweeds and most vascular terrestrial and marine plants, all of which have translocation systems for moving materials among plant portions. Unlike these other plants, which preferentially allocate chemical defenses to young tissues, D. ciliolata cannot readily translocate secondary metabolites. The growth-differentiation balance hypothesis suggests that actively dividing and expanding cells are less able to produce secondary metabolites. This hypothesis may help explain why older tissues are better defended than young, rapidly growing apices.
对褐藻网胰藻（Dictyota ciliolata）植物体内次生代谢产物浓度、营养价值、韧性以及对食草动物的易感性的变化进行了评估。当将同一植株的幼嫩顶端和较老组织以相同数量提供给食草性双足虾长手鼓虾（Ampithoe longimana）和海胆刺冠海胆（Arbacia punctulata）时，幼嫩顶端的被食量大约是较老组织的2倍。与幼嫩顶端相比，较不受欢迎的较老组织的亲脂性提取物口感较差，两种次生代谢产物的浓度显著更高（另一种次生代谢产物没有显著差异），可溶性蛋白含量多33%，韧性强233%。较老组织中较高水平的化学防御，而非组织韧性或营养价值，似乎是长手鼓虾偏好幼嫩顶端的原因。网胰藻幼嫩组织中化学防御水平低于较老组织的模式，与多核海藻以及大多数维管陆生和海洋植物中观察到的模式相反，这些植物都有用于在植物各部分之间运输物质的转运系统。与这些优先将化学防御分配给幼嫩组织的其他植物不同，网胰藻不能轻易地转运次生代谢产物。生长 - 分化平衡假说表明，活跃分裂和扩展的细胞产生次生代谢产物的能力较弱。这一假说可能有助于解释为什么较老组织比幼嫩、快速生长的顶端受到更好的防御。
