The role of Abscisic acid for root gravitropism and quiescent center maintenance in Arabidopsis thaliana : 애기장대에서 뿌리 굴중성과 QC 유지와 관련된 ABA의 역할

다국어 초록 (Multilingual Abstract)

The plant hormone abscisic acid (ABA) plays a role in root gravitropism and has led to an intense debate over whether ABA acts similar to auxin by translating the gravitational signal into directional root growth. We show evidence that ABA plays a role opposite to that of auxin, indicating that it is a negative regulator of the gravitropic response of Arabidopsis roots. ABA promotes root agravitropism in auxin transport mutants. Our data obtained from both vertically and horizontally placed seedlings show that ABA plays a negative role in root gravitropism. NPA in promoting root agravitropism, ABA did not induce auxin accumulation in the root meristem, suggesting that ABA and NPA act through different mechanisms. The root-curling phenotype induced by auxin transport inhibitors in wild-type plants may involve in the endogenous ABA.
We provide experimental evidence that ABA links to the maintenance of stem cells, which are vital for the function of meristems, in Arabidopsis root meristems. We show that ABA promotes the quiescence of the stem cells in the quiescent center (QC) and suppresses the differentiation of stem cells and their daughters in both the distal and proximal parts of root meristems. We also show that these two ABA regulations are mediated by distinct pathways and establish that five identified ABA signalling molecules, ABI1, ABI2, ABI3, ABI5 and ERA1, act in the former regulation and that ABA modulates WOX5’'s function in the suppression of stem cell differentiation in the distal part of root meristems.
Our results reveal a novel ABA regulatory property which offers an attractive framework for understanding how plants control meristem activity during vegetative growth and protect meristem functions under environment conditions and also demonstrate an important role of negative regulator of root gravitropism in Arabidopsis thaliana.

목차 (Table of Contents)

• Ⅰ. Introduction 16
• 1. Plant hormones 17
• 2. ABA 21
• 3. ABA synthesis pathways 22
• 4. ABA and lateral root development 26
• 5. ABA and gravitopism 27
• 6. ABA and plant meristem 31
• Ⅱ. Material and Methods 37
• Section A. Abscisic acid is a negative regulator of root gravitropism in Arabidopsis thaliana
• 1. Plant materials and preparation of media 38
• 2. Growth conditions 38
• 3. Root measures 39
• 4. Histochemical staining of GUS activity 39
• 5. Confocal microscopy 39
• Section B. Fluridone affects quiescent centre division in the Arabidopsis thaliana root stem cell niche.
• 1. Plant materials and preparation of media 41
• 2. Growth conditions 42
• 3. Confocal microscopy 42
• 4. Starch staining 42
• Section C. ABA promotes QC quiescence and suppresses stem cell differentiation in Arabidopsis root meristems
• 1. Plant materials and preparation of media 43
• 2. Growth conditions 44
• 3. DEX induction 44
• 4. Confocal imaging and light microscopy 45
• 5. Starch staining and histochemical GUS activity staining 45
• 6. Quantitative RT-PCR 46
• Ⅲ. Results 48
• 1. ABA promotes root agravitropism in auxin transport mutants 49
• 2. The effect of the auxin transport inhibitor naphthyl phthalamic acid
• (NPA) on root gravitropism is reduced in ABA-deficient mutants 55
• 3. Root-curling involves ABA 59
• 4. Fluridone promotes QC division in the Arabidopsis root meristem 64
• 5. ABA suppresses QC division in a dose-dependent manner 70
• 6. Fluridone changes cellular pattern of the stem cell niche 72
• 7. ABA inhibits QC division in Arabidopsis primary root meristems 74
• 8. ABA suppresses the differentiation of stem cells and their daughters
• in Arabidopsis primary root meristems 83
• 9. ABA regulates QC division independently of ethylene 97
• 10. ABA’s regulation of QC division involves ABI1, ABI2, ABI3,
• ABI5, ERA1, but not ABI4 99
• 11. ABA’s regulation of stem cell differentiation requires the activities
• of WOX5 and MONOPTEROS 105
• Ⅳ. Discussion 109
• 1. Nutritional signals are involved in the regulation of root growth movement 110
• 2. ABA promotes root growth by promoting QC quiescence and
• suppressing the differentiation of meristem and their daughters in
• root 113
• 3. The role of ABA in promoting QC quiescence reflects a general regulatory property of this regulator in suppressing cell division 116
• 4. ABA and QC maintenance in Arabidopsis root meristems 122
• Conclusion and Summary 124
• References 127