TY - JOUR
T1 - Integrating transient heterogeneity of non-photochemical quenching in shade-grown heterobaric leaves of avocado (Persea Americana L.)
T2 - Responses to CO2 concentration, stomatal occlusion, dehydration and relative humidity
AU - Takayama, Kotaro
AU - King, Diana
AU - Robinson, Sharon A.
AU - Osmond, Barry
PY - 2013/11
Y1 - 2013/11
N2 - Long-lived shade leaves of avocado had extremely low rates of photosynthesis. Gas exchange measurements of photosynthesis were of limited use, so we resorted to Chl fluorescence imaging (CFI) and spot measurements to evaluate photosyn-thetic electron transport rates (ETRs) and non-photochemical quenching (NPQ). Imaging revealed a remarkable transient heterogeneity of NPQ during photosynthetic induction in these hypostomatous, heterobaric leaves, but was adequately integrated by spot measurements, despite long-lasting artifacts from repeated saturating flashes during assays. Major veins (mid-vein, first- and second-order veins) defined areas of more static large-scale heterogeneous NPQ, with more dynamic small-scale heterogeneity most strongly expressed in mesophyll cells between third- and fouth-order veins. Both responded to external CO2 concentration ([CO2]), occlusion of stomata with Vaseline™, leaf dehydration and relative humidity (RH). We interpreted these responses in terms of independent behavior of stomata in adjacent areoles that was largely expressed through CO2-limited photosynthesis. Heterogeneity was most pronounced and prolonged in the absence of net CO 2 fixation in 100p.p.m. [CO2] when respiratory and photorespiratory CO2 cycling constrained the inferred ETR to ∼75% of values in 400 or 700p.p.m. [CO2]. Likewise, sustained higher NPQ under Vaseline™, after dehydration or at low RH, also restricted ETR to ∼75% of control values. Low NPQ in chloro-plast-containing cells adjacent to major veins but remote from stomata suggested internal sources of high [CO 2] in these tissues.
AB - Long-lived shade leaves of avocado had extremely low rates of photosynthesis. Gas exchange measurements of photosynthesis were of limited use, so we resorted to Chl fluorescence imaging (CFI) and spot measurements to evaluate photosyn-thetic electron transport rates (ETRs) and non-photochemical quenching (NPQ). Imaging revealed a remarkable transient heterogeneity of NPQ during photosynthetic induction in these hypostomatous, heterobaric leaves, but was adequately integrated by spot measurements, despite long-lasting artifacts from repeated saturating flashes during assays. Major veins (mid-vein, first- and second-order veins) defined areas of more static large-scale heterogeneous NPQ, with more dynamic small-scale heterogeneity most strongly expressed in mesophyll cells between third- and fouth-order veins. Both responded to external CO2 concentration ([CO2]), occlusion of stomata with Vaseline™, leaf dehydration and relative humidity (RH). We interpreted these responses in terms of independent behavior of stomata in adjacent areoles that was largely expressed through CO2-limited photosynthesis. Heterogeneity was most pronounced and prolonged in the absence of net CO 2 fixation in 100p.p.m. [CO2] when respiratory and photorespiratory CO2 cycling constrained the inferred ETR to ∼75% of values in 400 or 700p.p.m. [CO2]. Likewise, sustained higher NPQ under Vaseline™, after dehydration or at low RH, also restricted ETR to ∼75% of control values. Low NPQ in chloro-plast-containing cells adjacent to major veins but remote from stomata suggested internal sources of high [CO 2] in these tissues.
KW - Avocado
KW - Heterobaric anatomy
KW - Patchy stomata
KW - Photosynthetic induction
KW - Vaseline ™
KW - Xanthophyll pigments
UR - http://www.scopus.com/inward/record.url?scp=84887856043&partnerID=8YFLogxK
U2 - 10.1093/pcp/pct128
DO - 10.1093/pcp/pct128
M3 - Article
SN - 0032-0781
VL - 54
SP - 1852
EP - 1866
JO - Plant and Cell Physiology
JF - Plant and Cell Physiology
IS - 11
ER -