POTENTIAL EFFECTS OF UV-B ON PHOTOSYNTHES IS AND PHOTOSYNTHETIC PRODUCTIVITY OF HIGHER PLANTS - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 138

Table 2 . Growth and pigment parameters measured six weeks after planting for AMBIENT UV,
UV-A, UV-B, well watered (WW) and drought (D) treated pea plants in the field. Values are the
means of four replicate blocks. Leaf number is the number of true leaf pairs and leaf area includes
both true leaf pairs and associated stipules. DW, Dry weight. Flavonoid and anthocyanin pigment
relative contents were estimated from the absorbances at 300 ( A 300 ) and 530 nm ( A 530 ) respectively, of
acidified methanol extracts of the youngest fully expanded leaf and expressed on a leaf area basis.
Data partially from Allen et al. 23

Water Plant DW

(g)

Height
(cm)

Leaf
Number

Leaf Area
(cm 2 )

UV

AMB

WW 2.99 38.0 10.8 339

D 2.25 36.0 7.7 324

UV-A

WW 2.73 36.2 11.4 367

D 2.78 35.8 8.0 310

UV-B

WW 3.04 39.8 10.0 366

D 2.43 36.1 7.2 363

UV Water Root/shoot

(g g -1 )

Shoot
Number

Flavonoids
( A 300 cm -2 )

Anthocyanins
( A 530 cm -2 )

AMB

WW 0.155 1.75 4.78 0.527

D 0.170 1.08 4.66 0.576

UV-A

WW 0.157 2.08 4.50 0.491

D 0.185 1.50 5.17 0.612

UV-B

WW 0.158 1.75 5.10 0.504

D 0.176 1.67 5.25 0.642

This absence of UV-B effects on photosynthesis and biomass contradicts the
conclusion of many “square-wave systems”. However, the data from Mepsted et al. 29
and Allen et al. 23 support the findings of other modulated UV-B field experiments
which found no effects either on biomass accumulation in pea 30-31 , rice, barley 31 , oak 32 ,
wheat and wild oat 33 , or on photosynthetic parameters e.g. light-saturated CO 2
assimilation 34 , stomatal conductance 34 , maximum or steady-state I PSII 31,35 . The weight of
evidence coming from these modulated UV-B field experiments suggests that current
predictions for O 3 depletion will not adversely affect plant productivity and
photosynthesis in crops directly. The discrepancy between the results from
“square-wave” and modulated UV-B field supplementation systems does support the
contention that “square-wave” systems may exaggerate plant responses to UV-B
supplementation, as suggested by Fiscus et al. 36 . Caldwell et al. 35 demonstrated in the