The Role of Silicon in Alleviation of Iron Deficiency in Cucumber (Cucumis sativus L.)

Nedostatak gvožđa (Fe) predstavlja jedan od glavnih ograničavajućih faktora u proizvodnji useva širom sveta, koji značajno umanjuje prinos i kvalitet. Sa druge strane, koristan efekat silicijuma (Si) na rastenje i razviće biljaka, posebno u uslovima stresa, dobro je poznat u literaturi. Cilj ove teze je bio da se prouči mehanizam kako Si ublažava stres izazvan nedostatkom Fe kod dikotiledonih biljaka (strategija I usvajanja Fe), o kome se do sada ništa nije znalo. Kao model biljka odabran je krastavac (Cucumis sativus L.) kao vrsta koja akumulira Si. Izvršena su detaljna izučavanja mobilnosti Fe u apoplastu, biosinteze jedinjenja koja mobilišu Fe i njegovog daljeg usvajanja na bazi redukcije u korenu, zajedno sa ekspresijom gena uključenih u te procese. U nadzemnom delu biljke, proučavana je remobilizacija Fe iz starijih u mlađe listove, tako što su paralelno mereni distribucija 59Fe u listovima na različitim pozicijama i koncentracija helatora nikocijanamina (NA), zajedno sa ekspresijom gena za nikocijanamin sintazu (NAS) uključenu u njegovu biosintezu i YSL (eng. yellow stripe-like) transporter koji posreduju u transportu Fe-NA floemom. Ishrana Si uticala je na povećanu akumulaciju Fe u apoplastu i Fe-mobilizirajućih jedinjenja u korenu, kao i na stimulaciju mašinerije za usvajanje Fe. U listovima, Si je uticao na relativnu distribuciju Fe povećavajući remobilizaciju Fe iz starijih listova zbog povećane akumulacije NA i ekspresije YSL1, što je pospešilo heliranje Fe i njegovu retranslokaciju u mlađe listove. Ova teza pruža, po prvi put, objašnjenje mehanizma koji Si ispoljava u prevazilaženju nedostatka Fe, a koji se sastoji u povećanju rezervi Fe u apoplastu korena, njegove mobilizacije i trasporta iz korenu u izdanak, kao i poboljšane remobilizacije iz starijih u mlađe listove.Iron (Fe) deficiency represents a major limiting factor for crop production worldwide, affecting both crop yield and quality. Beneficial effect of silicon (Si) on plant growth and development, especially under stress conditions, is well documented in the literature. The objective of this thesis was to investigate the mechanisms of how Si ameliorates Fe deficiency in Strategy I plants, which has not been understood until recently. Cucumber (Cucumis sativus L.) was selected as a common model plant for Fe research and which is also known as a Si-accumulating dicot. Detailed analyzes of the dynamics of apoplastic Fe, biosynthesis of Fe-mobilizing compounds and reduction-based Fe acquisition were performed in roots along with the expression of relevant genes involved in these processes. At the shoot level, distribution of 59Fe was measured in the in leaves at different positions and developmental stages in parallel with the concentration of the Fe chelator nicotianamine (NA) and the gene expression of nicotianamine synthase (NAS) involved in its biosynthesis. The expression of yellow stripe-like (YSL) transporters mediating pholem transport of Fe-NA in shoot was also determined. Silicon nutrition increased the accumulation of apoplastic Fe and Fe mobilizing compounds in roots. In leaves, Si affected relative Fe distribution by enhancing Fe remobilization from old leaves via increased NA accumulation and expression of the YSL1, which stimulated Fe chelation and its retranslocation to younger leaves. This thesis for the first time elucidates the mechanism of Si-mediated alleviation of Fe deficiency stress, by increasing the root apoplastic Fe pool, enhancing its acquisition by roots and translocation to shoots and also remobilization of Fe from older to younger leaves