Leaf structure-function relationships and responses to plant hormones in non-seed plants

ABSTRACT. Non-seed plants are prosperous on Earth, but until now there are many mysteries about them in plant science. In the current thesis, non-seed plants were studied under two conditions: non-stressed and stressed. When under optimum conditions, leaf structural, chemical, and photosynthetic traits of non-seed plant species were studied to reveal the life strategy they chose for living. Compared to the seed plants, these early land plants tend to adopt a more conservative strategy by investing more resources to build up a robust body structure, sacrificing their capabilities to photosynthesize. Leaf density is found to be a fundamental trait (instead of the classical structure trait leaf mass per unit area) that represents structural characteristic of a plant leaf; thus, it helps to uncover trade-offs in a spectrum of interrelationships between different plant functional traits. When under stress (simulated by applying phytohormones), certain defense pathways in non-seed plants are activated. In general, non-seed plants behave similarly to seed plants in terms of both gas exchange characteristics and volatile organic compound emissions. However, there are differences. First, only four fern species out of nine close their stomata upon abscisic acid, showing a species-specific characteristic in this plant lineage; second, upon methyl jasmonate, one of the spikemosses Selaginella martensii emits a should-be time-consuming volatile compound linalool in a faster manner compared to the seed plants. Moreover, this spikemoss utilizes an alternative signaling pathway rather than the classical jasmonate pathway in seed plants.

Publication of this thesis is supported by the Estonian University of Life Science.

This study was partly funded by the European Commission through the European Research Council (advanced grant 322603, SIPVOL+), the European Regional Development Fund (Centre of Excellence EcolChange) and the Estonian Research Council (team grant PRG537). The equipment used in the study was partly funded by the ERDF (AnaEE Estonia and Plant Biology Infrastructure-TAIM) and by the Estonian Research Council (project TT5).

LÜHIKOKKUVÕTE. Eostaimed on Maal levinud, kuid neist teatakse palju vähem kui seemnetaimedest. Käesolevas lõputöös uuriti eostaimi tava- ja stressitingimustes. Optimaalsetes tingimustes uuriti eostaimede lehtede struktuurseid, keemilisi ja fotosünteetilisi tunnuseid, et mõista nende taimede elustrateegiaid. Võrreldes seemnetaimedega kasutasid evolutsiooniliselt vanad maismaataimed konservatiivsemat strateegiat, investeerides rohkem ressursse tugeva lehestruktuuri ülesehitamiseks ja andes seejuures järelefotosünteesivõimekuses. Leiti, et lehtede tihedus on oluline lehestruktuuri tunnus (klassikalise tunnuse “lehe mass pindalaühiku kohta” asemel), mis aitab avastada lõivsuhteid taimede funktsionaalsete tunnuste vahel. Fütohormoonide kasutamisega simuleeritud stressis aktiveerusid eostaimedes erinevad kaitsereaktsioonid. Üldjuhul käitusid eostaimed nii gaasivahetuse omaduste kui ka lenduvate orgaaniliste ühendite heitkoguste poolest sarnaselt seemnetaimedega. Siiski leiti töös ka erinevusi. Esiteks, ainult neli sõnajalaliiki üheksast sulgesid oma õhulõhed abstsiishappe toimel, mis näitab, et sellele hormooniline reageerimine on liigispetsiifiline tunnus. Teiseks, metüüljasmonaadi toimel eraldas selaginell Selaginella martensii seemnetaimedega võrreldes kiiremini tavaliselt aeglaselt eritatavat lenduvühendit linalooli. Lisaks kasutas see selaginell stressivastuses seemnetaimedes levinud jasmonaadi raja asemel alternatiivset signaalirada.